A sprawling Democratic bill expanding health, education and other benefits for veterans seems ready to clear an initial hurdle in the Senate. Yet the election-year measure faces an uncertain fate as Republicans try to make it smaller and find ways to pay for it.

The legislation, which sponsor Sen. Bernie Sanders, I-Vt., says would cost $21 billion over the coming decade, could confront GOP lawmakers with an uncomfortable campaign-season test over curbing spending for the nation’s 22 million veterans and their families. Most veterans groups support the legislation, and the voting bloc they represent is a potent one that both parties usually try to avoid offending.