For the tea-party coalition and its leaders, it’s a triumphant return to power inside the Beltway after an election cycle where they were minor players and a year on Capitol Hill in which they’ve occasionally fumbled. Republican leadership, which initially shrugged off the defunding cry, now faces a flush and angry grassroots operation.

“Turn on any political news show, read any magazine, and all they’re talking about is how conservatives want to defund Obamacare,” says Sal Russo, an adviser to Tea Party Express. “The Tea Party has matured from a protest movement to a collection of organized groups that know how to roll up their sleeves and engage in the political process.”

The GOP’s loyalists are less pleased. “It’s Republicans attacking Republicans, and I don’t think it’s healthy for the party,” says Brian Walsh, a former official at the National Republican Senatorial Committee. “These groups are spending hundreds of thousands of dollars against Republicans who simply disagree with their strategy.”