WASHINGTON (Reuters) - U.S. Senate Majority Leader Mitch McConnell on Tuesday said the U.S. debate on healthcare would continue, but said nothing about whether he would bring an Obamacare repeal bill to a vote. Opening the Senate, McConnell praised the bill sponsored by Republican Senators Lindsey Graham and Bill Cassidy, saying it contrasted sharply with Democratic proposals for “single-payer” healthcare. “It’s an important debate for our country. It’s one that will certainly continue,” McConnell, a Republican, said.   Three Republican senators have said they will vote against Graham-Cassidy. But Republicans can lose no more than two votes on the measure, leaving the bill with no clear path to advancing in the Senate.   