Democratic presidential candidate Hillary Clinton, left, and Republican presidential candidate Donal Trump. (AP photos)

Hillary Clinton and Donald Trump are scheduled to appear on the same stage early next month at a “commander-in-chief forum” devoted to national security, military affairs and veterans issues.

The Democratic and Republican presidential nominees will appear back-to-back Sept. 7 in New York at an event sponsored by the Iraq and Afghanistan Veterans of America and broadcast live in primetime on NBC and MSNBC, the sponsors announced Thursday.

Preparedness to be commander in chief has become a major issue in the presidential race, with Clinton and Trump questioning the other’s fitness.

On Monday, in a speech about fighting the Islamic State, Trump said Clinton “lacks the mental and physical stamina to take on ISIS and all of the many adversaries we face.”

Clinton, meanwhile, has touted the endorsements of a growing number of Republican military and national security figures who question Trump’s temperament and knowledge of international affairs.

The joint forum is scheduled ahead of the three more traditional debates between the two major-party candidates, the first of which is scheduled for Sept. 26.

Forum organizers said Clinton and Trump will field questions from NBC News personnel as well as an audience comprised mainly of military veterans and active service members.

Paul Rieckhoff, founder and chief executive officer of the veteran’s group sponsoring the forum, said it would “ensure that America’s next commander-in-chief, at least for one night, addresses our nation’s moral obligation to support and empower its 22 million veterans, our service members and our military families.”