There's a sensation building over the Democratic convention speech of Khizr Khan, a Pakistani-born Virginia lawyer whose son Humayun was killed in action while serving as a captain in the U.S. Army in Iraq in 2004.

In seven minutes on the national stage, Khan, a naturalized U.S. citizen who came to this country in 1980, excoriated Trump for proposals to build a wall along the Mexican border and to temporarily ban the entry of foreign Muslims into the U.S.

"Let me ask you: Have you even read the United States Constitution?" Khan said to Trump. "I will gladly lend you my copy. In this document, look for the words 'liberty' and 'equal protection of law.'"

"Have you ever been to Arlington Cemetery?" Khan continued. "Go look at the graves of the brave patriots who died defending United States of America — you will see all faiths, genders, and ethnicities. You have sacrificed nothing and no one."

Even before Khan's speech ended, Democrats and anti-Trump Republicans began to issue rhapsodic praise on social media and elsewhere. Video of the speech went viral, along with commentary that it was the best of the convention, the most moving, the most powerful, the most devastating to Trump, and so on. Khan, who ended with an exhortation to vote for Hillary Clinton, became an instant star of the campaign.

At the same time, some Trump supporters stirred outrage with foolish attacks on Khan. Ann Coulter tweeted, "You know what this convention really needed? An angry Muslim with a thick accent like Fareed Zakaria." The American Family Association's Sandy Rios said Khan's loyalty to the U.S. is in question. Then Trump himself downplayed the Khans' sacrifice in an interview with ABC News.

With a few obvious differences, the uproar bears some resemblance to a white-hot controversy more than a decade ago involving Cindy Sheehan, a California woman whose son Casey was killed in 2004 while serving in the U.S. Army in Iraq.

Sheehan became a media sensation when she attacked President George W. Bush over the war. Opponents of the war immediately took up her cause in their protests, and Sheehan became, for a while, ubiquitous in media reports of opposition to Bush and the war.

Some Republican Bush supporters (including Coulter) stirred outrage with foolish attacks on Sheehan, although in those pre-Twitter days there were fewer opportunities for a single comment to go viral.

Now, with Khan, the parents of another son killed in Iraq are in the middle of a national storm. But this one is over immigration. Like Cindy Sheehan, as the father of an American soldier killed in action, Khizr Khan has standing to do what he is doing. Those who disagree with him should never belittle his sacrifice or impugn his motives. But they can challenge his argument.

Khan's brief speech wasn't a finely-detailed case. But he suggested that Trump's Muslim ban and Mexican border wall proposals are unconstitutional. Specifically, Khan cited the words "liberty" and "equal protection of the law" in suggesting that Trump's policies violate the Constitution.

It's hard to know what Khan meant by suggesting a wall on the Mexican border would be unconstitutional. Perhaps it would be a bad idea, or it wouldn't work as Trump claims it would, but there's simply no sense in which a border wall violates the Constitution. (Some libertarians have argued that the use of eminent domain required to build a wall would violate property-owners' rights, but that's more complaining than constitutional argument — and besides, Khan didn't seem to be talking about property rights.)

Khan did not mention deportations, but regardless of exactly where Trump's illegal immigrant proposal stands at the moment, there is nothing unconstitutional about deporting people who are in the United States illegally.

As far as a Muslim ban is concerned, Trump has recently amended his proposal to focus on immigration from countries "compromised by terrorism." But assume that Khan was addressing Trump's original, more extensive, proposal: a temporary ban on foreign Muslims from entering the United States. By telling Trump to "look for the words 'liberty' and 'equal protection of law'" in the Constitution, Khan was suggesting that the ban would violate the 14th Amendment. This is the relevant portion of that amendment:

All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws.

The text makes clear that its protections apply to "all persons born or naturalized" in the U.S.; persons "subject to the jurisdiction thereof"; and persons "within its jurisdiction." None refers to foreign persons in foreign countries. Pakistanis in Pakistan, to take one example, regardless of religion, do not have U.S. constitutional rights. As far as "liberty," the other word mentioned by Khan, is concerned, the Constitution says the government may not deprive someone of liberty without due process of law, which of course means the government may deprive someone of liberty with due process of law.

Some of Trump's critics still insist that Trump has proposed banning all Muslims, including U.S. citizens, from entering this country. Last December, when Trump first proposed the Muslim ban, he called for a "total and complete shutdown" but made clear within hours that it would not apply to U.S. citizens, members of the U.S. military, and others with a legal right to be in the United States. If a ban covered all Muslims, including U.S. persons, then it would without question be unconstitutional. But that is not what Trump proposed. Now, Trump has limited his proposal to a temporary ban on immigration from some countries, which is also entirely constitutional. In addition, it's very likely such a move would survive constitutional challenge even if President Trump did it solely on his own executive authority.

It may be that building a wall, deporting illegal immigrants, and temporarily banning the entry of foreign Muslims are all terrible policies. But among the Democrats and anti-Trump Republicans touting Khan's performance there appears to be a belief that if something is a terrible policy, it must also be unconstitutional. That's not necessarily so.

It should be noted, though, that Trump's proposals are not unconstitutional according to the way the Supreme Court has interpreted the law for the last 225 years. If a President Trump acted on his proposals and was challenged in court — as he certainly would be — there would always be the possibility that the justices might make up some new reading of the Constitutional to invalidate the president's actions.

One last thing. Cindy Sheehan's son, Casey, and Humayan Khan died just 65 days apart in Iraq in 2004. The next year, when Sheehan became an idol of the antiwar cause in an increasingly bitter debate over Iraq, Democrats expressed great admiration for her.

Now, with Democrats having nominated a candidate who voted to authorize the Iraq war (only later to oppose it), against a Republican who regularly calls the war a disaster and says he opposed it from the beginning, another Gold Star parent, Khizr Khan, has become a cause — but in an entirely different context.

It seems unlikely that the Clinton campaign would have given the anguished parents of a son or daughter who died serving in Iraq the opportunity to tell the convention that the war should never have been authorized or fought. But when the Clinton campaign ran across Humayun Khan's story and realized how useful the Khans might be against Trump on the issues of Islam and immigration, the grieving parents were quickly invited to Philadelphia.

The Khans represent a small group. Humayun Khan was one of just 14 Muslim-Americans (the number was compiled by the House Homeland Security Committee) among the 6,885 U.S. troops who have died in Iraq and Afghanistan. But his parents' anguish is very real and their story very powerful. And it will undoubtedly be used against Trump many times between now and November.

Here, for the record, is the entire text of Khizr Khan's address to the Democratic convention:

Our thoughts and prayers are with our veterans and those who serve today.
Tonight we are honored to stand here as parents of Capt. Humayun Khan and as patriotic American Muslims with undivided loyalty to our country.
Like many immigrants, we came to this country empty-handed. We believed in American democracy — that with hard work and goodness of this country, we could share in and contribute to its blessings.
We were blessed to raise our three sons in a nation where they were free to be themselves and follow their dreams. Our son, Humayun, had dreams, too, of being a military lawyer. But he put those dreams aside the day he sacrificed his life to save the lives of his fellow soldiers.
Hillary Clinton was right when she called my son "the best of America." If it was up to Donald Trump, he never would have been in America.
Donald Trump consistently smears the character of Muslims. He disrespects other minorities, women, judges, even his own party leadership. He vows to build walls and ban us from this country.
Donald Trump, you are asking Americans to trust you with their future. Let me ask you: Have you even read the United States Constitution? I will gladly lend you my copy. In this document, look for the words "liberty" and "equal protection of law."
Have you ever been to Arlington Cemetery? Go look at the graves of the brave patriots who died defending United States of America — you will see all faiths, genders, and ethnicities. You have sacrificed nothing and no one.
We cannot solve our problems by building walls and sowing division. We are stronger together. And we will keep getting stronger when Hillary Clinton becomes our president.
In conclusion, I ask every patriot American, all Muslim immigrants, and all immigrants, to not take this election lightly. This is a historic election, and I request to honor the sacrifice of my son, and on election day, take the time to get out and vote, and vote for the healer, vote for the strongest, most qualified candidate, Hillary Clinton — not the divider. God bless you. Thank you.