Senate Democrats want at least four key witnesses, including Bolton and acting White House chief of staff Mick Mulvaney, to testify.

President Donald Trump's defense team member Ken Starr used the opposite argument defending the President's use of executive privilege than he did in the impeachment case against President Bill Clinton in 1998.

Alan Dershowitz, the 81-year-old Harvard Law professor hired by President Trump’s legal team, railed against House Democrats’ “vague and open-ended” impeachment charges Monday. “Purely non-criminal conduct, including ‘abuse of power’ and ‘obstruction of justice,’ are outside the range of impeachable offences,” Dershowitz told the Senate in his hour-long address. “That is the key argument I...

"Those Democratic caucus goers, will they be supporting vice president Biden at this point?” asked Sen. Joni Ernst.

The Senate impeachment trial isn’t exactly good press for President Donald Trump. But Senate Republicans says it’s also hurting former Vice President and 2020 hopeful Joe Biden.

The second day of the impeachment trial took a sharp turn, when Trump attorneys Pam Bondi and Eric Herschmann spent a significant portion of their time on the Senate floor arguing that Biden should be investigated for corruption.

Bondi primarily focused on Biden’s son, Hunter Biden, and his role on the board of Ukrainian gas company Burisma while his father was vice president and in charge of Ukraine matters. Trump's team has presented no evidence that Biden used his role as vice president to benefit his son nor alleged anything improper other than the "appearance of a conflict."

But Senate Republicans used the concerted attack on Biden to raise questions about his political viability.

“Iowa caucuses are this next Monday evening and I’m really interested to see how this discussion today informs and influences the Iowa caucus voters, those Democratic caucus goers, will they be supporting vice president Biden at this point?” asked Sen. Joni Ernst (R-Iowa).

“I was watching Elizabeth [Warren] and Bernie [Sanders] and Michael [Bennet] and Amy [Klobuchar] and they were really eyes wide open during that part of it," said Sen. John Barrasso (R-Wyo.), referring to the four senators vying for the Democratic nomination sitting as jurors in the trial. "I think it's going to be harmful. It can't be a positive. Certainly not in November if he's the nominee and I think even in terms of getting the nomination."

Over the course of the afternoon, Bondi, the former Florida attorney general, and Herschmann featured clips of the elder Biden talking about his work in Ukraine, as well as footage of his son's recent televised interview about Burisma.

Democrats impeached Trump last month on charges that he pressured Ukraine to investigate Biden and other Democrats in order to benefit his 2020 reelection. Trump defenders say his interest in pursuing a Biden probe was a genuine reflection of his concerns about corruption and that they viewed Biden suspiciously for seeking the removal of a Ukrainian prosecutor who was supposed to be investigating Burisma.

But witnesses told the House throughout the fall that the impression created by Trump's allies was false -- that in fact, Biden's attempt to remove Ukraine's top prosecutor was in support of U.S. foreign policy any backed by the international community. Far from investigating Burisma, they said, the prosecutor was sidestepping an investigation of the company and his removal made it likelier that Burisma would face a legitimate probe.

The Biden campaign and Senate Democrats pushed back vehemently against the Trump defense team’s arguments, and have long argued that the attacks against the former vice president have no basis in fact.

Andrew Bates, a spokesperson for Biden, said shortly after Bondi’s presentation that she was doing nothing more but spreading conspiracy theories that have been debunked by major news organizations, including the New York Times, the Wall Street Journal and the Washington Post.

"We didn't realize that Breitbart was expanding into Ted Talk knockoffs. Here on planet Earth, the conspiracy theory that Bondi repeated has been conclusively refuted,” Bates said in a statement. “Joe Biden was instrumental to a bipartisan and international anti-corruption victory. It's no surprise that such a thing is anathema to President Trump."

During the Senate trial, Bondi argued that she was merely responding to the arguments from House impeachment managers, who she said mentioned the Biden family during their opening arguments more than 400 times. But Senate Democrats saw nothing more than a political attempt to damage the former vice president.

“The first part just seemed to be a big 2020 campaign commercial list of the president's campaign highlights and bashing the Bidens,” said Sen. Chris Murphy (D-Conn.). “From the very beginning it seems as if the president was so focused on Joe Biden partly because he knew Joe Biden was a strong candidate.”

“Look at the hour when they did it,” added Sen. Jon Tester (D-Mont.) “It had nothing to do with what the president did.”

Both Murphy and Tester said it was unclear whether the attacks would hurt Biden.

Senate Democrats said that the criticism of Biden was long expected and note that so far he's been resilient. In the discussion around whether to bring witnesses into the impeachment trial, some Senate Republicans have said the Senate should bring in Hunter Biden if Democrats follow through on their demands to subpoena former Trump national security adviser John Bolton. Whether or not the Senate decides to bring in witnesses remains to be seen. Senate Democrats still need support from four Republicans to bring in Bolton.

Sen. Brian Schatz (D-Hawaii) said he was surprised the Trump team didn't spend the entire day attacking Biden.

"They alternated between making a serious legal case and accommodating the president's desire to exact revenge," Schatz said. "I was expecting it to be more maddening and more explosive."

Senate Republicans, however, defended the Trump team and argued they were merely responding to the presentation from House impeachment managers.

"Because Democrats raised it or the House managers raised it, I think the president's defense team thought they had to lay out the record to basically just show there's a reason to have questions,” said Sen. Ron Johnson (R-Wis.) “There are legitimate questions that remains outstanding. I thought it was totally appropriate.”

Burgess Everett, Kyle Cheney, Heather Caygle and John Bresnahan contributed to this report.