House Republicans should support a Democratic motion Thursday to open a formal, transparent presidential impeachment investigation and specify rules for the process.

Republicans who deny there is a reason at least for an investigation are pushing a blatantly dishonest line. If Republicans examine all the evidence and then determine nothing impeachable occurred, that is their prerogative. Clearly, though, the allegations at issue are manifestly serious, and President Trump’s already-known behavior was at least objectionable if not impeachable.