Inside the Senate GOP resistance to Trumpcare Sens. Ted Cruz, Rand Paul, and Mike Lee are among those against the bill.

 -- Just as House Speaker Paul Ryan was rolling up his sleeves to give a presentation on the House Republican Obamacare replacement plan, on the other side of the Capitol, senators offering a full-throated defense of the bill were scarce.

The House blueprint, which Ryan referred to as a "three-pronged approach" Thursday, includes some provisions that various Republican factions oppose; most notably, a plan to provide tax credits to individuals, which some critics have said amounts to a new entitlement, and an eventual cap on the amount of Medicaid funding states can receive, which worries some Republicans whose states accepted an Obama-era Medicaid expansion.

Sen. Lindsey Graham said some of his colleagues believe the bill does not do enough to address the underlying causes of increased insurance premiums, one of the chief reasons Republicans say they need to replace the Affordable Care Act with a new plan.

"I have got concerns because people I respect in this area believe that it's fallen short," he said.

The Senate has 52 Republicans and needs a simple 51-vote majority to pass the Obamacare replacement package. They can have up to two party members defect, as Vice President Mike Pence can cast a tie-breaking vote. While the bill is still working its way through the legislative process, ABC News counts at least 10 senators who have either said outright they can’t support it in its current form, or have voiced uncertainty.

Three senators who met with Vice President Mike Pence today and at least in part discussed health care reform, Sens. Rob Portman, R-Ohio, John Thune, R-South Dakota, and Pat Roberts, R-Kansas, expressed lukewarm sentiments about the House bill.

Portman's home state of Ohio is one of 32 that accepted the Affordable Care Act's Medicaid expansion, which brought in more recipients by raising the percentage of the poverty level above which people could join. He said he reiterated to Pence that he was concerned the bill, which would eventually cap states’ Medicaid payments, would harm his constituents.

"I raised the same concerns I've raised all along," Portman said.

Portman, along with three other senators whose states expanded Medicaid, is part of a growing group of senators who have expressed concerns about the bill in its current form because of the way it deals with Medicaid.

"They’re getting it done," Thune said of the House’s process. "My guess is that kind of the basic sort of components of the bill -– Medicaid reforms and refundable tax credits and things like that -– are all elements that I suspect will be in any package."

He did not address the fact that many Republicans on both sides of the aisle, including the conservative House Freedom Caucus, have voiced concerns with exactly those provisions.

Sens. Ted Cruz, R-Texas, Rand Paul, R-Kentucky, and Mike Lee, R-Utah, have also said they oppose the bill because of its tax credits. Last week the three members launched a coordinated Twitter offensive, each tweeting, ""2 yrs ago, the GOP Congress voted to repeal Obamacare. That 2015 repeal language should be the floor, the bare minimum. #FullRepeal."

An eighth senator, Susan Collins, of Maine, says she balked at the fact that the bill would end federal payments to Planned Parenthood because the women's health service also provides abortions.

Roberts, the third senator in the Pence meeting, said he told the administration officials present that they could "maybe sell this a little better" and emphasize GOP-favored concepts that have broader support like the ability to buy insurance over state lines.

Trump sought to sell the deal when he tweeted assurances that the bill’s drafting was going along smoothly.

But a few hours earlier, Sen. Tom Cotton, an Arkansas Republican who has supported Trump more than many of his colleagues, voiced his own skepticism of the bill using Trump's preferred medium.

Cotton later told ABC News' Jon Karl in an interview that he feared the current version of the House bill might make the health care system worse, not better.

White House spokesman Sean Spicer addressed the Republican senators' concerns during the daily briefing, saying that as the White House continues to advocate for the "comprehensive three-pronged approach," (using the same language as Ryan), including via local media, radio and local community leaders, more people will get on board with it.

But at the very least, Spicer added, “no matter where you are, especially on the conservative side, you cannot possibly believe that the current healthcare system is an effective program."

That was the position of at least one Republican senator, Chuck Grassley, R-Iowa, who indicated he wouldn't be picky about what sort of Obamacare replacement makes it to the Senate floor.

"I'm inclined to support anything because of Obamacare being such a failure," he said.