Not all of those falsehoods are lies, but even media outlets have grown comfortable labelling some of the most high-profile ones as lies.
Many of Trump's falsehoods, in fact, deal with the same topics Cohen was lying about, including hush-money payments to women and the pursuit of a Trump Tower Moscow. If we can't trust Cohen for this reason, what about Trump?
But this wasn't the only attack that could blow back in the White House.
Early on, the ranking Republican of the committee, Representative Jim Jordan, suggested the hearing shouldn't even take place.
In doing so, he alleged that Cohen might be the first congressional witness to be called back after having lied to Congress.
The problem: Earlier this month, the Trump Administration's new special envoy to Venezuela, Elliott Abrams, testified in front of Congress. He pleaded guilty in 1991 to … wait for it … lying to Congress. He was later pardoned by George H.W. Bush.
Similarly, Republicans sought to cast doubt on the motivations of Cohen's lawyer, Lanny Davis, who is a longtime ally of Bill and Hillary Clinton. Representative Jody Hice, R, got Cohen to admit that Davis was working free, and he asked Cohen whether it might have been Davis who persuaded him to testify publicly against Trump.
But if lawyers who are working free and have potential conflicts rouse suspicion, Trump and his personal lawyer would seem to have some questions to answer. Rudy Giuliani is not accepting any compensation for that same role, and as the New York Times has noted, he is courting business abroad.
Perhaps the most high-profile attack on Cohen over the past 24 hours, though, came from Representative Matt Gaetz, R, who yesterday tweeted a suggestion that Cohen had "girlfriends" he might want to tell his wife about.
In defending the tweet before he eventually deleted it and apologised, Gaetz said he was merely "challenging the veracity and character of a witness." The claim carried no evidence.
But Trump's alleged marital infidelity is something that followed him long before the alleged affairs with Stormy Daniels and Karen McDougal — starting with his courtship of Marla Maples, who would become his second wife, while he was still married to his first wife, Ivana.
And the last problem for Republicans is that, while Cohen has clearly lied to further his own interests, many of the lies he's admitted to have a common characteristic: They were done on Trump's behalf.
Whether Trump directed him to lie is important, and Cohen has made it clear that Trump was well aware of his alleged misdeeds with regards to Trump Tower Moscow and the hush-money payments.
If Cohen was such an unsavory and irredeemable character, what about the President who was clearly involved in these things, to one extent or another, and hired him to be his "fixer?"
The GOP has engaged in a grand bargain with Trump.
He has power that is instrumental in enacting a conservative agenda and confirming judges who Republicans like, but in exchange they need to regularly forfeit the moral high ground.
Often this takes the form of simply turning a blind eye to Trump's rougher edges or trying to explain why his falsehoods, misdeeds and objectionable behaviour aren't important.
But that bargain and the loss of the moral high ground comes with a cost.
And a bunch of Republicans attacking the President's own former lawyer as a liar who can't be trusted was an extremely tricky bit of theatre today.
