President Joe Biden has said his work to support Ukraine in its fight against Russia is among his signature accomplishments, but now the fate of funding America's ally has become enmeshed with the most vexing policy challenge he’s faced in office: immigration.

As Senate Republicans blocked the advance of tens of billions of dollars in military and economic assistance for Ukraine Wednesday, President Joe Biden berated their tactics as “stunning" and dangerous.

The Senate’s decision to block aid to Ukraine is not necessarily definitive, but it is a blow to the Democrats and infuses new urgency into the two parties’ ongoing talks to reach an agreement on immigration policy. Those negotiations reached an impasse over the weekend.