David Brat, who scored a major upset in defeating the No. 2 Republican in Congress in Tuesday's primary in Virginia, labeled immigration as a major point of contention between himself and Cantor, crediting his own hardline stance in his victory.
Some advocates fear that House Republicans will interpret the primary's results as a sign they should avoid entangling themselves with immigration legislation before November's congressional elections.
"Many Republicans will react reflexively and say: 'Let's not touch this issue,'" said Frank Sharry, executive director of the America's Voice immigration advocacy group.
Seeing the chances of legislation dim with Cantor's defeat, immigration advocates cast doubt on Wednesday on President Barack Obama's strategy to hold back on executive action until he has given the Republican-controlled House of Representatives a last chance to act.
Obama said last month he would be delaying much-anticipated changes to the nation's deportation policy in hopes the House would act on passing comprehensive immigration before this August's legislative recess, which is seen as the last practical window for passing a bill under this Congress.
"If there were doubts before, this is sort of the lid to put on it. We now need the president to act," said Eddie Carmona, campaign manager for PICO National Network's Campaign for Citizenship.
Obama, speaking at a fundraiser on Wednesday, rejected the view that Cantor's loss spelled the end of immigration reform.
"It's interesting to listen to the pundits and the analysts and some of the conventional wisdom talks about how the politics of immigration reform seem impossible now. I fundamentally reject that," Obama said.