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Over the last few days, Sen. Pat Toomey (R-Pa.) has spoken with several of his Republican colleagues about the possibility of having two witnesses appear during President Trump's impeachment trial, three GOP officials told The Washington Post.

One of the witnesses would be called by Republicans, and the other by Democrats, the officials said. The Senate is scheduled to vote later this week on whether to have witnesses in the trial, with Democrats urging lawmakers to allow testimony from witnesses with firsthand information on Trump and the Ukraine scandal. On Sunday night, The New York Times reported that former National Security Adviser John Bolton writes in his forthcoming book that Trump said he wanted to withhold military aid to Ukraine until officials there launched investigations into former Vice President Joe Biden and his son, Hunter.

Toomey, who is not up for reelection until 2022, is close to Senate Majority Leader Mitch McConnell (R-Ky.), but not President Trump or his top aides, the Post reports. Toomey has discussed his "one-for-one" proposal with Sen. Mitt Romney (R-Utah), the Republican officials said, as well as Sen. Susan Collins (R-Maine). On Monday morning, Romney said Bolton's testimony was "relevant," adding that it is "important to be able to hear from John Bolton for us to be able to make an impartial judgment."