Update: The Clinton campaign is now up with an ad featuring conservatives questioning Trump's foreign policy. It closes with a brutal quote from conservative columnist Charles Krauthammer saying he wouldn't want Trump to have the nuclear codes.

Hillary Clinton's campaign released this ad August 2, which features Republicans denouncing GOP presidential nominee Donald Trump. (Hillary Clinton)

Below, we explain why this is an issue for Trump:

Earlier this week, Joe Scarborough offered a pretty striking secondhand account of Donald Trump's foreign policy acumen — or rather, his lack thereof.

"I'll be very careful here," the MSNBC host said, before passing along some hearsay. "Several months ago, a foreign policy expert on an international level went to advise Donald Trump, and three times he asked about the use of nuclear weapons. Three times, [Trump] asked — at one point, 'If we have them, why can't we use them?'"

The Trump campaign is strongly denying this account, but it does highlight a very interesting dichotomy when it comes to Trump. And that's this: Americans love Trump when it comes to defeating the Islamic State. When it comes to the nuclear button, though, they'd apparently prefer he come nowhere near it.

In a Fox News poll, Americans prefer Trump to Hillary Clinton by 9 points — 51 percent to 42 percent — when it comes to "destroying terrorist groups like ISIS." But when asked more broadly about who is better on the issue of terrorism, it's a tie. More broadly still, on foreign policy, Clinton leads by 16 percentage points, 55 to 39.

And then we get to the nuclear button. On this issue, Americans favor Clinton by a whopping 22 percentage points, 56 to 34. That's up from the 11-point advantage she had on this issue in May.

All the usual caveats apply here. This is one poll, and it comes shortly after a Democratic National Convention that has provided a real and substantial (but perhaps temporary) bump for Clinton's campaign. Trump's numbers, meanwhile — along with his performances on the stump — are getting worse and are causing a panic.

But the numbers match almost completely a Quinnipiac University poll from June, when Americans preferred Trump by 13 points on handling the Islamic State but said they'd rather have Clinton in charge of the nuclear button by a 19-percentage-point margin, 54 to 35.

The widely divergent views of Trump's foreign policy strengths are pretty telling when it comes to views of his temperament and preparedness for office. Trump says he'll be much tougher on the Islamic State than the Obama administration and that he's going to "bomb the s--- out of ISIS," and apparently that's what Americans want.

As long as those bombs aren't nuclear.