WASHINGTON (AP) — Republican Marco Rubio's potential defection over a tax credit for low-income parents put a speed bump into GOP leaders' drive to push their big tax package through the Senate, but it's a complication that's likely to be resolved. The Florida senator declared Thursday that he'll vote against the $1.5 trillion bill unless House and Senate negotiators expand the tax credit that low-income Americans can claim for their children. That puts the Republicans' razor-thin margin in the Senate closer to the edge.