'Zero doubt we're getting witnesses': Trump's legal team bracing for GOP defections
President Donald Trump (MSNBC)

If at least four Senate Republicans vote to subpoena additional witnesses and documents -- that could trigger a domino effect.

Sources close to Senate Majority Leader Mitch McConnell will likely try to reach an agreement with Minority Leader Chuck Schumer if it appears likely that 51 senators will vote for new testimony, with demands for GOP witnesses, rather than going to a vote, reported Axios.

The most likely GOP defectors remain Sens. Susan Collins (ME), Mitt Romney (UT), Lisa Murkowski (AK) and Lamar Alexander (TN), but that could put new pressure vulnerable senators up for re-election such as Cory Gardner (CO), Thom Tillis (NC), Martha McSally (AZ), Rob Portman (OH), Joni Ernst (IA) and Pat Toomey (PA).

“You don’t want to be one of the first four, but no one gives a f*ck about the fifth vote,” one GOP senate aide told Axios. “Especially for all of the 2020-ers. If it turns into a free vote, why wouldn’t you vote for witnesses?”

Trump's legal team seems to understand the trial won't end without new witnesses, but Republicans seem intent on putting Hunter Biden under oath.

“There is zero doubt we’re getting witnesses," said a source close to Trump's legal team. "If there’s witnesses, we’re calling witnesses. We just need 51 votes."

"There's no way they're going to bring in John Bolton and Mick Mulvaney and not bring in our people," that source added. "That would just be completely unfair and it would undermine their whole reason for having witnesses in the first place.”