House Republicans unveiled a spending bill Saturday that would keep federal agencies funded through Sept. 30, pushing ahead with a go-it-alone strategy that seems certain to spark a major confrontation with Democrats over the contours of government spending.

Democrats decried the measure as a White House power grab, leaving it unclear whether the legislation could pass.

Still, Republican leaders face a tricky math situation. Any spending legislation will require 217 votes to pass if all members are present and voting. That means Republicans, with 218 members in their current majority, can only afford one defector. Any more than that, and the bill is tanked.