The John Adams rap Watsky does here was originally part of the off-Broadway version of Hamilton’s “The Adams Administration.” It was cut from the show, but lives on via the Mixtape. In this video, you can watch LMM and members of the original cast perform a version of it:

In essence, this song is a rap version of the Letter from Alexander Hamilton, Concerning the Public Conduct and Character of John Adams, Esq. President of the United States. Originally sent to 200 of his fellow Federalists on the eve of the election of 1800, the letter can be summarized as a fifty-page rant about Adams’s many shortcomings, followed by an unconvincing pro forma endorsement of Adams’s reelection. A copy somehow made its way to the Democratic-Republicans, who gleefully reprinted and distributed it widely. The letter ended up permanently damaging Hamilton’s standing in the Federalist Party, splitting the Federalist vote between supporters of Adams and supporters of Hamilton’s ally Pinckney, and clearing the way for the Jefferson–Burr ticket’s victory and the events described in The Election of 1800.