Rubio's defection threatens Senate GOP's margin on tax bill

Senate Finance Committee Chairman Orrin Hatch, R-Utah, center, talks with Sen. Chris Coons, D-Del., left, as they leave the chamber following a vote, on Capitol Hill, in Washington, Thursday, Dec. 14, 2017. (AP Photo/J. Scott Applewhite)Washington • Republican Sen. Marco Rubio declared Thursday he will vote against the GOP’S sweeping tax package unless negotiators expand its child tax credit, jeopardizing the Republicans’ razor-thin margin as they try to muscle the $1.5 trillion bill through Congress next week.

Rubio wants to increase the portion of the basic $2,000-per-child tax credit that would go to low-income families. In the current bill, families that pay little or no income tax would…