Following Sunday's New York Times report - which cited sources revealing that a manuscript of Bolton's forthcoming book states that Trump told him in August 2019 that withholding military aid to Ukraine was tied to investigations into Democrats - Graham made it clear he wanted to hear more but has not been swayed that Bolton should necessarily be called as a witness in the Senate impeachment trial.
Mr. Trump's defence team, however, side-stepped the Bolton issue as they defended their client in the Senate on Monday.
The elephant in the room on the second day of Mr Trump's defence arguments was Mr Bolton whose unpublished book manuscript, according to the New York Times, included disclosures that go to the heart of the abuse of power charge against Mr Trump.
Trump's defense has largely skirted the reported revelations from a draft of a book written by former National Security Adviser John Bolton. That could rob him of the chance to crow about exoneration in front of the assembled members of Congress.
Trump is expected to be acquitted in the 100-seat Senate, where Republicans hold 53 seats and a two-thirds majority is needed to remove him from office under the U.S. Constitution. Schumer also indicated Democrats would reject any effort at a so-called witness swap with Republicans.
Senior Republican lawmakers continued to resist the idea of witnesses. A Democrat run impeachment inquiry had found that Mr Trump conditioned the aid to Ukraine and a crucial White House meeting with his Ukrainian counterpart, Volodymyr Zelenksy, on the Ukrainians announcing investigations into former Vice President Joseph Biden, the Democrat frontrunner for the White House and his son, Hunter, who was on the board of Ukrainian energy company Burisma.
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New Orleans Pelicans player Josh Hart sent a tweet using a hashtag of Bryant's nickname, "Mamba". "#Mamba", the tweet read. McCollum added: "Please don't tell me this is true". @kobebryant you were my biggest fan, but I was yours.
Republican Senators Mitt Romney of Utah, Susan Collins of ME and Lisa Murkowski of Alaska are among the senators openly discussing whether to join Democrats to subpoena Bolton and perhaps others to testify.
He said it was "somewhat absurd" to accuse the White House of trying to hide the call. Still, several Republicans said the revelation in his yet-to-be published book that Trump directly linked aid for Ukraine to politically motivated investigations raised questions that should be answered.
Ukrainian officials have said they found no indication that Hunter Biden had broken any law. The political implications were illustrated by Iowa Republican Senator Joni Ernst, who wondered if Trump's lawyers' presentation could hurt Biden's candidacy and his showing in Monday's caucuses.
Trump's team has previously said he was well within his constitutional authority to press Zelensky to investigate the Bidens as part of what he says was an anti-corruption drive. Biden campaign spokesman Andrew Bates dismissed Ms Bondi's allegations, saying they had been widely discredited. Braun said he's not convinced that Trump's conduct was impeachable, even if the Bolton allegations are true.
Trump's legal team was due to deliver its third and final day of arguments urging his acquittal starting at around 1 p.m. (1800 GMT), with plans to finish by dinner time.
Starr said that after the Clinton impeachment both parties decided "enough was enough" and allowed the independent counsel statute allowed to expire.