WASHINGTON — With a Senate vote on the GOP health care bill delayed until at least next week, opponents are using the additional time to build on their efforts to defeat the measure.

“Every day that the Senate doesn’t repeal the Affordable Care Act and gut Medicaid is a day that makes it less likely they’ll be able to pass it,” said Ben Wikler, Washington director of the progressive group MoveOn that is opposing the bill.

At least one major fissure could be forming. Sen. Ron Johnson, R-Wisc., who said last week he would vote on the critical procedural vote that needs the support of 50 senators to even begin debate on the health care bill, has now said that he might vote against it after he learned that Senate Majority Leader Mitch McConnell told senators concerned about deep cuts to Medicaid that the changes are far in the future and probably would never be enacted.

"I did find the story about leader McConnell’s comments about Medicaid reforms just too far in the future probably never being enacted — I found those pretty troubling and so that might put the motion to proceed vote in jeopardy," Johnson said.

Senate Majority Leader Mitch McConnell had planned for a vote on the Better Care Reconciliation Act this week but was forced to delay it after Sen. John McCain, R-Ariz., underwent surgery for the removal of a blot clot near his brain over the weekend. McCain is unable to return to Washington while he recovers and, with two GOP senators already opposed to the bill, Senate leaders can't lose a third and must have every other Republican vote in order to pass the bill.

The additional time is giving opponents a chance to organize more rallies, protests, call-in campaigns, mass emails, door-to-door canvassing and sit-ins at senators’ Washington offices to pressure Republicans to vote against the a bill that is already in jeopardy.

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At least 33 people were arrested Monday during protests on Capitol Hill where activists filled hallways outside of GOP offices to pressure key members to vote against the bill.

In addition to the two Republicans opposing the bill — Sens. Rand Paul, R-Ky., and Susan Collins, R-Maine — there are at least eight other GOP senators who have voiced serious concerns with it.

Related: McConnell Delays Health Care Vote as McCain Recovers From Surgery

Paul said the delay would make it more difficult for leadership.

“I think the longer the bill's out there, the more conservative Republicans are going to discover that it's not repeal. And the more that everybody's going to discover that it keeps the fundamental flaw of Obamacare,” Paul said on CBS News’ “Face the Nation” Sunday.

White House Press Secretary Sean Spicer said that President Donald Trump has been working hard to persuade wavering senators.

"He’s been very active on the phone. He’s going to continue to meet with senators and he’ll have some ... senators over tonight. He’s been very active over the weekend," Spicer said during Monday's off-camera briefing.

Sens. Lamar Alexander, R-Tenn., John Cornyn, R-Texas, Roy Blunt, R-Mo., Steve Daines, R-Mont., and James Lankford, R-Okla. are among those who will have dinner with Trump at the White House Monday evening.

But missing from the list of attendees are some of those most critical to the bill's passage. At least three skeptics — Rob Portman, R-Ohio, Mike Lee, R-Utah, Shelley Moore Capito, R-W.Va. — have not been invited to attend the dinner.

Senate Democrats have been pressuring Republicans to hold open hearings on their bill. They’ve stalled all judicial nominations, including non-controversial ones, slowing the process to a crawl until Republicans hold health care hearings.

Senate Minority Leader Chuck Schumer sent a letter with Sens. Patty Murray, D-Wash., and Ron Wyden, D-Ore., sent a letter to Senate Majority Leader Mitch McConnell, asking him to use the extra time to hold hearings and allow a complete score from a Congressional Budget Office before holding a vote.

“Given your decision to delay the vote on the Better Care Reconciliation Act, we request that you use this additional time to hold public hearings so that Senators can invite impartial experts, including patients, to testify on the policies in the bill, especially the radically conservative Cruz/Lee proposal released to the public only five days ago,” Schumer, Murray and Wyden wrote.

Collins agrees that the process should be more transparent.

“At the end of the day, I don't know whether it will pass. But I do know this. We should not be making fundamental changes in a vital safety net program that's been on the books for 50 years," Collins said on CNN’s “State of the Union" Sunday, "without having a single hearing to evaluating what the consequences are going to be.”