Donald Trump spoke about immigration in Phoenix tonight, after meeting with Mexican President Nieto earlier in the day. Here are a few brief thoughts:

School Vouchers

"If we spent less on illegal immigrants, we would have more money for school vouchers, which many people want," Trump said.

Yes, in theory, this could happen. If illegal immigrants cost the country billions of dollars a year, then those billions of dollars could give hundreds of thousands of students school vouchers.

But school voucher programs aren't typically funded with extra money on top of other school spending. They're usually funded by taking a portion of a student's existing per-pupil public funding and allowing them to use that funding toward private school tuition. That ultimately leaves public schools better off in a per-pupil sense, because they retain some of the funding even after the student leaves.

That said, if the government saves money by ending illegal immigration, why use it on school choice if it's so easily funded other ways? Why not use the savings to pay down the debt, cut taxes or spend on something else Trump finds to be important?

The Wall

"We will build a great wall along the southern border," Trump said to thunderous applause.

Just a reminder: a southern border wall is wildly implausible, even if Mexico does pay for it.

If Trump is elected, he can't just sign an executive action on day one that builds the wall. Like any other spending project, spending authorization would have to go through the House and Senate, and through their respective committees. Even Trump's plan to make Mexico pay for the wall through tariffs and visa fees needs authorization from Congress.

If a bill gets signed into law, the wall has to go through a labyrinth of federal bureaucracies: at least nine cabinet-level departments, the EPA and other federal agencies. The Department of Homeland Security would oversee the project. The Army Corps of Engineers would study the project's needs and design. Several Department of the Interior agencies would be involved in environment concerns. Affected landowners will inevitably end up in court, and the Department of Justice will have to defend any property seizures that occur. And that's just part of the process. Who knows how many years, or decades, it might take to build?

Polls

Looking at the polls, it doesn't seem like Trump's speech is going to help him with the voters he needs to win the election.

Trump says he's going to win the African-American vote. But only 25 percent of African Americans want immigration decreased from its present level, according to a June 2016 Gallup poll. Perhaps surprising to most, Hispanics are actually more likely to say immigration should be decreased from its current level, with 35 percent saying so.

Trump might say there were nuances in his speech that implied immigration overall is a good thing, but the tone of the speech was rather harshly anti-immigration, and media coverage is sure to reflect that tone. But fewer than 20 percent of African-Americans and Hispanics say immigration is a bad thing for the country.

It's possible Trump's speech will sway some of these people's opinions, but the margins are so wide it's unlikely to make a difference.

Jason Russell is a commentary writer for the Washington Examiner.