As a congressman who led the first impeachment of President Trump, Mr. Schiff relished his role in the resistance. Now a senator, he must protect his state’s interests at a perilous time.

Sen. Adam Schiff (D-Calif.) said Friday that President Trump invited him and California’s other Democratic senator, Alex Padilla, on a visit to California amid the wildfires ravaging in Los Angeles — an offer Schiff said he turned down only because the Senate is voting on high-profile Trump nominees.