But the spiraling Ukraine conflict has pointed up how far the power of Congress in the foreign policy arena has fallen since the death of Senator John McCain, the move of Senator Joseph R. Biden Jr. off Capitol Hill and to the White House, and the rise of a brand of partisanship that extends well beyond the water’s edge.

This week, loud voices emerged urging President Biden to act forcefully to counter Russian aggression. But other lawmakers have used the crisis for partisan advantage, castigating the president and blaming the Biden administration for President Vladimir V. Putin’s assault on his neighbor.

Perhaps more telling is the relative quiescence, from both Democratic and Republican leaders in Congress, who are hobbled by divisions in their ranks and seemingly content to let the White House take the lead, the credit or the blame…

It is … consistency that is fraying, Mr. Salter said, and cheap shots for attention are not helpful. Republicans who stood silent as Mr. Trump launched a sustained assault on NATO and leaned toward Mr. Putin now speak of Mr. Biden’s weakness toward Russia. Leaders have failed to condemn isolationist voices in the party such as Mr. Trump and Representative Marjorie Taylor Greene of Georgia, who questioned on Twitter, “What is with these neocons drooling over our 18 year old men getting blown to pieces in war?”