When a two-decade-old video clip of Lindsey Graham blared out of a monitor on the Senate floor Thursday afternoon, it was clear that this was going to be an edgier sort of day in the impeachment trial of Donald John Trump. Graham, one of Trump’s most vehement defenders in the Senate, was shown in the video, younger and with much more hair, confidently announcing that of course a President can be impeached for transgressions that are not covered by criminal law. He was, in other words, a strong witness for the House Democratic managers who are prosecuting the case against Trump. As Thursday went on, so were Trump’s F.B.I. director and Attorney General, two of his former Russia advisers, his former Homeland Security director, and a Harvard law professor who’s now serving on Trump’s legal team. Welcome to Trolling Day at the Trump trial.

During hours of arguments, on Thursday afternoon and late into the night, that were meant as a prebuttal to Trump’s forthcoming defense, the House managers sought to anticipate and undercut the arguments of the President’s lawyers. The best witnesses they called were all the President’s men. The managers presented video clip after video clip demolishing the President as a mere parrot of Russian propaganda, who repeated Russian-inspired falsehoods about the 2016 campaign and his Presidential rival Joe Biden, even as he withheld crucial aid to Russia’s enemy, Ukraine. There was “no information” to support Trump’s insistence that Ukraine, not Russia, interfered in the 2016 U.S. election; it was “completely debunked,” a “fictional narrative” divorced from anything having to do with U.S. foreign policy or its national interest. Trump’s accusers were not #NeverTrump Republicans or Democrats. They were senior officials in the Trump Administration. It was devastating.

So it was surprising when I noticed several Republican senators becoming visibly excited during the presentation. One of the House managers, Sylvia Garcia, of Texas, had just begun talking, and many of the senators’ seats were empty—I counted more than a dozen—when she started. But her topic soon turned out to be of great interest to Graham and other staunch Trump defenders: the matter of Joe Biden and what he did or didn’t do in Ukraine. As Garcia talked of Biden, Graham, who had ducked out of the chamber and actually missed his video-star turn a little while earlier, turned to his neighbor, John Barrasso, of Wyoming, to whisper something. Graham grinned and wrote down notes on his legal pad. A row behind him, Ted Cruz, of Texas, had an uncharacteristic look of delight on his newly goateed face. A couple rows in front of Graham, Rand Paul, of Kentucky, actually raised his arm in the air and pointed emphatically.

It seemed odd that Republicans should be excited by any aspect of the Democratic argument. On the issue of Biden, Garcia was attempting to methodically dismantle the claims that Biden had corruptly demanded the firing of Ukraine’s former prosecutor general in order to protect his son, Hunter Biden, who was then serving on the board of the Ukrainian energy company Burisma. “The allegations against Vice-President Biden are groundless,” Garcia said. She then recounted several lies and misrepresentations that have been advanced on Trump’s behalf, showing how he had specifically demanded investigations of the Bidens by the Ukrainian President and never mentioned the more noble goal of taking on “corruption” in Ukraine. She also covered the evidence that Trump had pushed Ukraine to “smear” Biden without caring whether there was an actual investigation. Citing the testimony of Trump’s own Ambassador to the European Union, Garcia said Trump’s goal was only that there be a public announcement of an investigation, to embarrass one of his toughest potential Democratic challengers in 2020.

But the Republicans were not reacting to the information Garcia described—information that has been well covered in the course of the impeachment proceedings. They were responding to what they saw as the opportunity created by Garcia’s presentation: By talking so much about Biden, wasn’t she offering the Senate a reason to call Biden and his son as witnesses? Sure enough, that is exactly the idea that some of the senators and Trump’s lawyer Jay Sekulow promoted during a break in the trial. “They have opened the door,” Sekulow told reporters. “It’s now relevant.” (Graham, for his part, later told reporters that he would resist the effort to call Biden.) “WOW,” Josh Hawley, another one of the Republicans who perked up when Garcia spoke, tweeted. “House managers make extended argument that Hunter Biden’s work w/Burisma entirely appropriate & no conflict of interest w/ Joe Biden getting rid of prosecutor that had jurisdiction over Burisma. If we call witnesses, gonna need to hear from both Bidens.”

This was not exactly on the level, of course. Cruz, Hawley, and others had been pushing Republican leaders on this point for weeks, as it became clear that the matter of whether to call witnesses had become the main, and arguably only, suspense surrounding the trial. Democrats insist that the Senate can only have a fair trial if it demands Trump Administration documents and witnesses who the President blocked from the House. Next week, they only need four Republicans to join with them to get the chance. But Republicans, fearing that they may lose the vote, are eager to extract a price. There is talk of a John Bolton-for-Biden trade. (This has been adamantly denied by Senate Democratic Leader Chuck Schumer, although the Washington Post has cited “Democratic officials” as having had discussions about it.) Every time the House managers mention the former Vice-President, Republicans will use the occasion to demand his testimony, no matter how irrelevant it is to the question of whether Trump abused the power of his office. On Saturday, Trump’s legal team will begin their case. I have no doubt that we will be hearing a lot about Joe Biden.

The 2020 Presidential campaign is casting a long shadow over the Trump impeachment trial, not least because Trump is the only President to run for reëlection while facing such a proceeding. Republicans, of course, constantly bring this up, arguing that voters, and not senators, should decide whether Trump should remain in office, and pointing out that voters will have the opportunity to do so a mere ten months from now.

But the Democratic Presidential race, which begins in just eleven days, with the Iowa caucuses, is even more immediately affected by the trial. Will Biden’s fortunes be harmed by his unflattering cameo in the matter? Or will he perhaps be helped by the fact that his major rivals in the Democratic race will miss the final few days of campaigning in Iowa in order to attend the entire duration of the trial?

Sitting in the Senate press gallery this week, I’ve spent hours observing the Democratic candidates, four of whom are on Trump jury duty. Amy Klobuchar, of Minnesota, who has staked her campaign on spending time in Iowa, which she is no longer able to do, sits in the back row and chats amiably with her neighbor, Delaware’s Chris Coons. She dashes off to the MSNBC or CNN cameras on the short breaks. One aisle over sits Michael Bennet, of Colorado, a long-shot candidate who waited patiently on Thursday morning to talk to the press throng in the Senate basement before the day’s proceedings began. Elizabeth Warren, the Massachusetts Democrat whose fortunes in the Presidential race have risen and fallen, sits in the front of the chamber, and her head is often bowed over a white legal pad. She has taken to drinking a glass of milk in the afternoon, and, when I watched her on Thursday, she was attentively turning the pages in a printed handout of the House managers’ presentation that the senators had been given.