SALT LAKE CITY — Despite personal pleas from Vice President Mike Pence and the Senate's assistant Republican leader, Texas Sen. John Cornyn, Utah's Sen. Mike Lee remains undecided on the Senate GOP's health care bill.

The Utah Republican's office confirmed he made it clear during telephone conversations with the vice president on Thursday and the Senate leader on Friday that he's still unsure whether he will vote to advance the bill next week.

The pressure is on Lee and the handful of other Republican holdouts on the bill intended to repeal and replace the Affordable Care Act, better known as Obamacare, because Senate leaders can afford to lose only one more GOP vote.

With Senate Democrats unanimously opposed, it would take just three Republicans to stop the bill. Two, Sens. Susan Collins of Maine and Rand Paul of Kentucky, already have announced they're voting against allowing the bill to be debated.

Lee and Sen. Ted Cruz, R-Texas, had been working together on what they called the Consumer Freedom Amendment, intended to allow health insurers to offer some limited, lower-cost plans that don't comply with Obamacare requirements.

But it's apparently not clear to Lee whether the language just added to the bill adequately addresses his concern that insurers should be allowed to separate customers into different coverage pools so healthier people can pay lower premiums.

Until Lee is satisfied the bill does what he wants, he seems to be making it clear he won't commit to supporting it.

In a statement issued Thursday, Lee said the new bill "is substantially different from the version released last month, and it is unclear to me whether it has improved." He said he'd need time to study whether "it does enough to lower health insurance premiums for middle-class families.”

His stand follows recent reports of his shift from "bomb thrower" to consensus builder on health care, a reference to his 2013 efforts with Cruz to stop funding for Obamacare that resulted in a costly federal government shutdown.

Chris Karpowitz, co-director of BYU's Center for the Study of Elections and Democracy, said Lee is in a tough position.

"He's under enormous pressure, enormous pressure, from the White House and from Republican leaders. No member of Congress wants to be the vote that scuttles a major initiative of the party or of the president," Karpowitz said.

Still, the political science professor said, Lee may well have plenty of company if he joins the Republican senators already opposed to the bill.

"My guess is it will either pass very narrowly or it will fail pretty substantially. It's not going to be a big victory, where they get anything more than Republicans," Karpowitz said.

He said the GOP senators are right to be cautious, especially given reports from federal experts that millions of people would lose their health care coverage and others may end up paying higher costs.

"The health care bill is a Republican effort to make good on a promise they have been making for a number of years," he said. But passing it puts them in the same positions Democrats ended up after the passage of Obamacare.

"Once you pass a bill, you are then responsible for what happens afterward. We certainly saw that with Obamacare, for better and for worse," Karpowitz said. And the Senate bill is already "incredibly unpopular."

That means for Lee "there can be a political benefit to opposing a bill that has extremely low levels of public support," Karpowitz said, even if he's attempting to act out of sincere concerns over policy.