Donald Trump delivered a strong speech Monday on thwarting terrorists and crushing ISIS while cleverly disguising it as an address on national security policy.

For once in recent days, Trump didn't get too clever. He lashed out at President Obama and Hillary Clinton for allowing Iraq to become fertile soil for the creation of ISIS. He didn't claim they had "founded" ISIS—that was Trump's position last week—only that their policies had allowed the terrorist group to flourish.

So the speech marked a sorely needed improvement in Trump's credibility. By failing to reach a status of forces agreement with the Iraqi government and then pulling the last contingent of American troops out of the country, Trump said Obama and Clinton in effect "launched ISIS on the world stage."

And Trump did advocate a new policy. He promised to "chart a new course" in fighting ISIS and halting "the spread of radical Islam." If elected president, Trump said he would put together a broad coalition of countries, including NATO members and Russia, to crush ISIS. Among his specific goals would be blocking the terrorist outfit's access to the internet.

With Trump, terrorism and immigration are twin issues. So it was no surprise when he outlined tough new rules in dealing with immigrants. He labeled them "extreme vetting." If anyone had doubts, this made it clear he would be far tougher with visa seekers than would Obama or Clinton.

The speech was delivered to a pro-Trump crowd in Youngstown, Ohio. The audience broke into chants of "Trump, Trump, Trump" a few times and also "U-S-A, U-S-A, U-S-A." This was unusual for a policy event, but the event served as a campaign rally as well. Besides, it was Trump who spoke.

Politically speaking, the speech was a plus for Trump. Terrorism and Clinton are major issues in the campaign and he addressed both in one big swoop. We're sure to hear more from him on this.

But foreign affairs and national security are at the core of another matter affecting Trump. His weakness in this area has been cited by Clinton and Democrats and even some Republicans as grounds for declaring him unfit to be president.

Last week, 50 former officials who worked on foreign policy and national security in Republican administrations from Nixon to George W. Bush said he lacked the "personal qualities" required in a president. In a letter, they said Trump "lacks the character, values, and experience to be president."

That wasn't all. "Unlike previous presidents who had limited experience in foreign affairs, Mr. Trump has shown no interest in educating himself," the ex-officials wrote. Worse, "he lacks self-control and acts impetuously."

The unfitness issue can't be dealt with in a speech or two. But Trump needs to address it. How? He must deliver serious speeches on critical world affairs. And then avoid wandering off into more trivial subjects in subsequent events.

He's been unable to stick to the high road of substantive issues so far in the campaign. Trump has refused to act "presidential," saying voters would find that boring. The Youngstown offered a bit of it. A lot more is needed.