WASHINGTON, July 25 (Reuters) - The U.S. Senate planned a critical vote on Tuesday on the seven-year Republican effort to repeal Obamacare, with Senator John McCain making a dramatic return to the U.S. Capitol to cast a potential deciding vote while battling brain cancer.
Senate Majority Leader Mitch McConnell scheduled a 2:15 EDT (1815 GMT) vote on whether to open debate on repealing Democratic President Barack Obama's signature healthcare law, but the outcome remained in doubt.
In the face of united Democratic opposition, McConnell can only afford to lose the backing of two of the 52 Republican senators. McCain returned from his home in Arizona, where he was recuperating from surgery and fighting a brain tumor, to provide a key vote to move forward on the Republican effort to unwind the 2010 Affordabloe Care Act, commonly known as Obamacare.
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"Today's vote to begin debate is the first step, and we should take it," McConnell said on the Senate floor, adding that Americans were "counting on us to do the right thing." He said the debate would be a "robust" process that would allow additional ideas on healthcare.
Senate Democratic Leader Chuck Schumer warned Republicans not to vote to open debate. "No one knows the plan that is being cooked up in the Republican leader's office," he said on the Senate floor.
He charged that McConnell's intention was to get the Senate to pass "anything" so that they can get to a conference with the House of Representatives, which has already passed a bill, and then repeal Obamacare. "Do not fall for the ruse," he said.
PRESIDENT STEPS UP PRESSURE
A loss on Tuesday would force Senate Republican leaders, who have struggled to amass support for their version of an overhaul, to find another strategy or move on to other legislative matters, such as tax reform.
Republican President Donald Trump has been increasingly critical of Republican senators for being unable to pass a bill. He kept up the pressure on Tuesday in a series of early-morning tweets, after chastising them at a White House event on Monday.
"After 7 years of talking, we will soon see whether or not Republicans are willing to step up to the plate!" he tweeted, praising McCain for coming back to Washington to cast his vote.
The tally in the divided chamber was expected to be extremely tight, making McCain's return critical to the repeal effort. He was diagnosed with an aggressive form of brain cancer earlier this month after surgery to remove a blood clot.
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Another possible holdout, Republican Senator Rand Paul, said he would vote to open debate on the bill because McConnell had promised the Senate would take up a straight repeal of Obamacare. Paul had opposed the Senate's replacement bill, which he said contained too much spending and bailouts for insurance companies.
Some senators said it was time to either tackle the issue on the Senate floor or move on to other matters.
"Now it's time to fish or cut bait," said Republican Senator Mike Rounds. "Let's get on with it. We have a lot of other things to do."
(Additional reporting by Amanda Becker, Richard Cowan; Writing by John Whitesides; Editing by Mary Milliken and Jonathan Oatis)