Why Biden did the debate throwdown, Trump agreed, and the risks for each side

Candidates debate when they have to debate.

That’s why Donald Trump didn’t during the primaries.

That’s why Joe Biden, battling abysmal poll numbers, surprised everyone yesterday by agreeing to two debates.

And why Trump, who’s been demanding a side-by-side comparison – he had even floated debating on my show – immediately accepted.

BIDEN’S TEAM IS AFRAID TO ‘LET HIM LOOSE’: LUCY CALDWELL

With a speed that raised questions about whether it was "rigged," both camps agreed within a couple of hours to do the faceoffs on CNN on June 27, and on ABC Sept. 10. (Four networks were deemed eligible.) CNN has already announced Jake Tapper and Dana Bash as moderators.

While key details remain to be worked out, Trump appears to have agreed to two key Biden conditions. And this is not a man who likes others dictating the rules.

First, Biden doesn’t want an audience. He doesn’t want Trump, who draws huge crowds at rallies, whipping his supporters into hooting and hollering. (Trump said he wanted big venues for "excitement.") The president wants a quiet debate focused on policy.

Second, Biden wants a mute button. That is, when one candidate is speaking for the allotted 60 or 30 seconds, the other’s mike is shut off. This is to prevent a replay of their first debate in 2020, when Trump was constantly interrupting or talking over Biden and moderator Chris Wallace. The former president can’t be thrilled about that.

CROSS-EXAMINATION THROWS MICHAEL COHEN OFF BALANCE, BUT BELABORS POINT THAT HE HATES TRUMP

This all went public at 8 a.m. Eastern yesterday morning, when Biden posted a short and snarky video:

"Now he’s acting like he wants to debate me again. Well, make my day, pal."

By the way, the man doesn’t make a very convincing Clint Eastwood.

"I’ll