Sen. Mitt Romney said Monday that it's "increasingly likely" that more Republicans will join calls to seek testimony from Bolton in Trump's impeachment trial, with the former national security adviser's new revelations throwing into doubt how Trump's trial will proceed.

And Sen. Susan Collins (R-Maine) -- who has signaled that she is open to supporting witnesses, as she did in former President Bill Clinton's 1999 trial -- said it will "strengthen the case" for witnesses. Sen. Lisa Murkowski (R-Alaska) added she was "still curious" what Bolton has to say.