House emissaries delivered to the Senate on Jan. 25 an article of impeachment against former President Donald Trump, setting the stage for an unprecedented trial of an ex-chief executive. As they were sworn in as jurors on Tuesday, Republican senators appeared to be splitting into three groups: those arguing Mr. Trump’s actions do not warrant impeachment; those open to convicting him; and those claiming that the former president cannot be tried because he is no longer in office. It is with this last camp that Mr. Trump’s fate likely resides. Most GOP senators voted unsuccessfully on Jan. 27 to force a debate on the constitutionality of trying Mr. Trump.

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