DURING THE House Judiciary Committee’s first impeachment hearing Wednesday, legal scholars said President Trump was guilty of grave abuse of his office and warned that declining to impeach him would invite more brazen behavior from Mr. Trump and future presidents. A dissent came from George Washington University law professor Jonathan Turley, whom Republicans called to testify. He avoided defending Mr. Trump’s actions on their merits. But he argued they were not impeachable crimes and insisted the Democrats should spend more time gathering evidence before moving the process forward. He was half-right.