The Senate headed into the second day of opening arguments from President Donald Trump's defense team in his impeachment trial on Monday.

Monday's proceedings, which began at 1 p.m. ET, come after The New York Times reported that former national security adviser John Bolton claims Trump personally told him he would withhold military aid to Ukraine until it launched politically motivated investigations targeting his rivals.

The revelation shatters the defense team's key argument against impeachment: that there are no firsthand witness accounts about the president directly confirming a quid pro quo.

Scroll down to watch the trial and follow Insider's live coverage.

Visit Business Insider's homepage for more stories.

President Donald Trump's Senate impeachment trial continued Monday as his defense team delivered more opening arguments. White House counsel Pat Cipollone is spearheading Trump's team, which also includes the president's personal lawyer, Jay Sekulow.

The defense is expected to argue its case for roughly eight hours on Monday and wrap up opening arguments on Tuesday.

The House of Representatives impeached Trump last month for abuse of power and obstruction of Congress. Both charges relate to his efforts to coerce Ukraine into launching politically motivated investigations targeting former Vice President Joe Biden, a 2020 Democratic frontrunner, and the Democratic Party as a whole.

While doing so, the president withheld $391 million in vital military aid to Ukraine, as well as a White House meeting that Ukrainian President Volodymyr Zelensky desperately sought and still hasn't gotten.

After the defense rests their case, senators will have 16 hours to submit written questions to the defense team and the seven House impeachment managers who prosecuted the case against Trump.

The Senate will then decide whether to subpoena additional documents or witness testimony, which requires a 51-vote majority.

Monday's proceedings come after The New York Times reported on an unpublished manuscript of former national security adviser John Bolton's upcoming book that threw a wrench into the president's defense.

According to The Times, Bolton claims Trump personally told him he would withhold Ukraine's military aid until Zelensky agreed to deliver politically motivated investigations targeting the Bidens.

Bolton's reported revelation directly undercuts the defense's argument that there are no firsthand witnesses who can say Trump himself confirmed a quid pro quo with Ukraine: military aid in exchange for political favors.

C-SPAN and TV networks are relying on the Senate's live feed of the trial.

C-SPAN is airing the trial at cspan.org.

You can watch the trial here:

Scroll down for Insider's live coverage of the hearing: