Moderate Senate Democrats threatened to scuttle healthcare legislation if their demands aren't met, while more liberal members warned their party leaders not to bend. The dispute among Democrats foretells of a rowdy floor debate next month on legislation that would extend healthcare coverage to roughly 31 million Americans. Republicans have already made clear they aren't supporting the bill. One major sticking point is a provision that would allow Americans to buy a federal-run insurance plan if their state allows it. Moderates say they worry the so-called public option will become a huge and costly entitlement program and that other requirements in the bill could cripple businesses.