“I don’t think the Biden administration wants to embark on a costly arms race when it has so many other priorities,” said Angela E. Stent, the director of the Center for Eurasian, Russian and East European Studies at Georgetown University. Russia was also a party to the 2015 Iran nuclear deal negotiated under the Obama administration, which Mr. Trump withdrew from in 2018 and Mr. Biden says he wants to rejoin. While the Obama administration engaged with Russia on a range of other issues, such as short-lived cease-fires in Syria and a negotiated settlement in Ukraine, others have emerged or gained new urgency over the past four years, including the climate crisis and the coronavirus pandemic, putting new pressure on Moscow to cooperate. 