There is no evidence that the elder Mr. Biden, while serving as vice president, improperly intervened in Ukraine to benefit his son. But the president’s advisers are betting that many voters will ignore the complexities of the allegations and absorb a simple message about a father using his influence to help his son, a senior Trump campaign official said…

But the prospect of a public airing of the White House’s corruption claims lasting into the primary season worries some Democrats, who see a parallel to Republican efforts to tarnish Hillary Clinton over her email practices in the run-up to the 2016 election. That campaign, they say, proved how damaging a constant stream of insinuations and accusations from Mr. Trump and his allies can be.

“The tactic is very similar,” said Karen Finney, a Democratic consultant and former Clinton campaign senior spokeswoman. “Republicans were doing all they could to amp up the questions about her emails. They didn’t necessarily argue the facts. All they had to do was throw in the question to raise doubts.’’