Republican senators, who have refused to allow witnesses in the Senate impeachment trial of President Donald Trump thus far, are reportedly shaken in their resolve after the New York Times published claims from an unpublished manuscript of Bolton’s book, which contains explosive accounts of Trump’s direct involvement in the Ukraine scheme.

Politico reported on Monday morning that its Republican sources believe the situation may have shifted following Bolton’s allegation that Trump told him $391 million in military aid to Ukraine was incumbent upon Ukraine’s assistance with his desired investigation into 2020 candidate Joe Biden.

The sources told Politico that Republican senators will plan their next move during its conference lunch on Monday.

Unnamed GOP sources also told Axios that there’s a possibility four Republican senators may break from the Senate GOP caucus’ stonewalling of witnesses in the trial in wake of the manuscript. Democrats need four GOP defections to successfully bring in crucial witnesses, such as Bolton.

Axios’ sources also said that the White House and GOP leaders will continue fight against having Bolton testify for fear that “if one witness is allowed, the floodgates are open” and that Democrats’ push for Secretary of State Mike Pompeo and acting White House Chief of Staff to testify will “intensify” if Bolton’s testimony ties the two administration officials to Trump’s Ukraine scheme.