President Donald Trump threatened Sen. Rand Paul (R-K.Y.) on Twitter after he opposed the recent efforts to repeal Obamacare. (Bill Clark/CQ Roll Call/Getty Images)

President Donald Trump singled out Sen. Rand Paul for opposing Republicans' latest efforts to repeal the health care law, warning that a vote against it would come with political consequences.

"Rand Paul, or whoever votes against Hcare Bill, will forever (future political campaigns) be known as 'the Republican who saved ObamaCare,'" Trump wrote on Twitter Friday.

The Kentucky Republican is so far the only GOP member of the Senate to come out firmly against the plan put forward by Sens. Lindsey Graham of South Carolina and Bill Cassidy of Louisiana. Paul has called the bill "Obamacare Lite," complaining that it does not go far enough to remove the 2010 health care legislation.

"Make no mistake – Graham-Cassidy keeps Obamacare funding and regulations in place," Paul wrote in an op-ed for Fox News this week. "Oh, it rearranges the furniture a bit, changes some names, and otherwise masks what is really going on – a redistribution of Obamacare taxes and a new Republican entitlement program, funded nearly as extravagantly as Obamacare."

Paul was re-elected for his second term in 2016, and will not face voters again until 2022.

But several others have expressed serious reservations about the bill, which Senate Majority Leader Mitch McConnell, R-Ky., said he plans to bring up for a vote next week.

Like Paul, Sens. John McCain of Arizona and Lisa Murkowski of Alaska were re-elected in 2016 and are therefore mostly immune to threats about their next campaigns. McCain's concerns have primarily been rooted in the rushed manner in which the bill has been pushed towards a vote. Murkowski has said she is considering the bill's impact on Alaska but has opposed previous repeal efforts because of proposed cuts to Medicaid funding that Graham-Cassidy also makes.

Sen. Susan Collins of Maine also has said she has a number of concerns about the bill, and is up for re-election next year. But she is said to be considering a run for governor instead, when a willingness to cross party lines would be more likely seen as an asset in a state that regularly elects members of both parties as well as independents.

Republicans have until the end of September before the special budget reconciliation rules that allow them to pass health care legislation with just a simple majority expire. Their 52-seat majority means they can afford for Paul and one other Republican to vote against Graham-Cassidy and it would still pass, with the help of a tie-breaking vote from Vice President Mike Pence.