Though the bulk of the presentations were geared toward exciting Trump's allies, there was at least one instance in which Herschmann attempted to appeal directly to Romney, who has already indicated he wants testimony from Bolton, who said he’d be willing to testify if subpoenaed. Herschmann played a clip of Obama debating Romney — then the GOP nominee for president — in 2012. In the clip, Obama mocked Romney for saying Russia was America's top geopolitical foe. Herschmann made eye contact with Romney, whose seat is in the back corner of the chamber, several times while he repeatedly invoked his name. Romney visibly smirked while his colleagues turned to face him.

Trump's team also took direct aim at Democrats' heavy reliance on the role of Trump’s personal attorney Rudy Giuliani in their case against the president. Democrats charged that Giuliani aided Trump's pressure campaign in Ukraine by ginning up smears against an anti-corruption U.S. ambassador, Marie Yovanovitch, and prompting Trump to remove her.

Trump attorney Jane Raskin offered a short presentation defending Giuliani's role — earning plaudits from the former New York City mayor on Twitter — by referring to him as an "internationally recognized expert on fighting corruption" and accusing Democrats of using his efforts in Ukraine as a "colorful distraction" to undermine Trump.

Perhaps most notably, the Trump legal team mostly ignored the new bombshell claims from Bolton that have injected new uncertainty into the trial.

“We deal with transcript evidence. We deal with publicly available information. We do not deal with speculation, allegations that are not based on evidentiary standards at all,” Jay Sekulow, Trump’s lead personal attorney for the trial, said as he opened up the second day of his team’s opening arguments at the Senate’s trial.

Bolton reportedly wrote in his forthcoming book that Trump told him in August that he wanted to withhold $391 million in military assistance to Ukraine until the country's president, Volodymyr Zelensky, agreed to share information pertaining to the investigations.

Former Harvard law professor and noted criminal defense attorney Alan Dershowitz, another member of the president’s legal team, mentioned Bolton by name late Monday night as he was wrapping up his presentation — but it was the only direct reference to the former national security adviser all day.

“Nothing in the Bolton revelations, even if true, would rise to the level of an abuse of power or an impeachable offense,” Dershowitz said.

But Trump's lawyers, led by Sekulow and White House counsel Pat Cipollone, indicated early on that instead of addressing Bolton’s reported account of his conversations with Trump, they would continue presenting a defense of Trump's conduct toward Ukraine — batting aside the House's charges that Trump pressured Ukrainian officials to launch baseless investigations of his Democratic adversaries.

“They say their case is overwhelming and uncontested. It is not. They say they have proven each of the articles against president trump. They have not,” White House deputy counsel Michael Purpura said. “The facts and evidence of the case the house managers have brought exonerate the president.”

Trump attorney Patrick Philbin made the most concerted case against witnesses, but only made passing references without mentioning Bolton by name.

"[T]he right conclusion is not that this body, this chamber, should try to re-do everything, to start bringing in new evidence and bring in witnesses," he said.

Senators also heard from Kenneth Starr, the former independent counsel who pushed for Bill Clinton’s impeachment. Starr, a member of the president’s defense team, delivered lofty remarks comparing impeachment to “domestic war” and “hell.”

Dershowitz closed Trump’s defense late Monday, arguing that both of Democrats' articles of impeachment — abuse of power and obstruction of Congress — are not legitimate impeachable offenses.

But Bolton's revelation presents an existential threat to the Trump defense, which has maintained for months that Democrats could not produce a single witness who could assert, with firsthand knowledge, that Trump linked the aid freeze to the investigations he sought. Bolton’s reported account also undercuts the White House’s justification for the hold on aid — that Trump wanted to pressure other countries to contribute to Ukraine’s defense, too.

So far, Republicans have mostly cast aside Bolton’s reported account, with some suggesting Bolton was just trying to boost his book sales and others saying the claims are nothing new. Democrats, meanwhile, have renewed their calls for testimony from Bolton and other officials, including additional documents that the White House withheld during the House’s inquiry last year.

Though the Democratic-led effort has sputtered in recent days, Romney said he thinks it is “increasingly likely that other Republicans will join those of us who think we should hear from John Bolton."

Bolton’s reported account also highlights the rapidly unfolding nature of the case against Trump, even since the House’s Dec. 18 vote to impeach him on two charges. An indicted associate of Trump’s personal lawyer Rudy Giuliani, Lev Parnas, provided text messages and sat for media interviews; internal White House documents describing turmoil over Trump’s decision to withhold Ukraine aid continued to emerge; and a nonpartisan congressional watchdog declared the hold unlawful.

Trump took the reins of his own defense after midnight on Monday, denying Bolton's reported account.

“I NEVER told John Bolton that the aid to Ukraine was tied to investigations into Democrats, including the Bidens,” he tweeted. “In fact, he never complained about this at the time of his very public termination. If John Bolton said this, it was only to sell a book.”

Hours later, Trump falsely claimed that Democrats never sought Bolton's testimony in their impeachment inquiry last fall. Democrats asked for Bolton to appear on Nov. 7, but he declined, initially deferring to Trump's direction.

Bolton has since said he would appear for testimony before the Senate if he is subpoenaed; but at least four Senate Republicans would need to join with all Democrats in order to issue that subpoena.

Trump's denial underscores another Democratic demand: that the Senate seek contemporaneous documents that the president has blocked, too. Bolton, a notoriously prolific note-taker, told other witnesses to document and report their concerns about Ukraine to their superiors, and Democrats are confident he would have kept an account of his interactions with Trump.