LOS ANGELES — When Joe Biden gave his victory speech after winning a series of key states in Super Tuesday, his son Hunter Biden, a Los Angeles resident, was nowhere near the scene.

With the former vice president now effectively in a one-on-one race with Vermont Sen. Bernie Sanders for the Democratic presidential nomination, the younger Biden’s absence was conspicuous. Hunter Biden’s business dealings in Ukraine were part of the fact set in President Trump’s impeachment. And unlike Joe Biden’s late son Beau, a Delaware attorney general, Hunter’s name is almost never mentioned on the campaign trail.