WASHINGTON — The U.S. Senate on Thursday rejected competing proposals by Republicans and Democrats to address a looming healthcare crisis, leaving some 24 million Americans vulnerable to significantly higher insurance premiums beginning on Jan. 1 when a federal subsidy expires.

Barring any late breakthroughs, Congress will begin an end-of-year holiday recess sometime next week and not return until Jan. 5, after new premiums are locked in for those who had relied on the Affordable Care Act enhanced subsidy.

In back-to-back votes largely along party lines, Democrats and Republicans blocked each other's bill.

The House of Representatives might attempt to pass some sort of legislation next week, which has not yet been unveiled. Even if it were to pass, Senate Democrats, and possibly some Re

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