Four years ago, he claimed Clinton’s use of a private email server as secretary of state endangered national security and alleged she used her government connections to enrich her family through the nonprofit Clinton Foundation. For many voters, the insinuations underscored doubts about the integrity of Clinton and her husband, the former president.

Polls suggest an uphill climb for a reprisal against Biden. Fewer voters dislike Biden than they did Clinton. And in 2016, voters who had negative views of both candidates overwhelmingly broke for Trump; for now, they favor Biden.

There are other inherent limitations to Trump’s effort to repeat his 2016 strategy.

The FBI investigated Clinton’s use of the email server and, while it did not bring charges, the fallout was politically damaging. But while the optics of the younger Biden’s lucrative work in China and with a Ukrainian gas company have frustrated some Democrats, no one has charged either father or son with any wrongdoing.