"I think that Paul Ryan's selling him a bill of goods that he didn't explain to the President, and the grassroots doesn't want what Paul Ryan is selling," the Kentucky Republican told CNN.
Paul was one of several lawmakers who took the stage in 20-degree weather outside of the Capitol, rallying conservatives to stand firm against the Republicans' health care bill that's making its way through the House. Conservatives feel that the bill doesn't go far enough in repealing Obamacare.
He urged voters to call other conservative members of the Freedom Caucus and urge them to "bring down the Paul Ryan plan," something he later called "Ryancare" to reporters.
"This is the very beginning of the battle, not the end of the battle," Paul said at the rally, which was hosted by the conservative group Freedomworks.
"But I promise you they will not negotiate until they discover they don't have our votes," he added. "But more importantly, they need to discover they do not have your votes."
Hitting back, Ryan told CNN's Jake Tapper on "The Lead" that he finds Paul's remarks "kind of puzzling," arguing that Republicans campaigned on the health care bill last year, and he took issue with Paul's argument that the "grassroots doesn't want" it.
"Frankly I think that's kind of an insulting remark to the President -- as if he doesn't know what he's doing," Ryan said.
The speaker said the White House is working "hand in glove" with the Republican plan.
"We think this is a smarter way to go," Ryan told Tapper. "The alternative is the status quo, and the status quo is in the middle of a collapse."
But Paul — who was among a group of conservative senators that went to the White House on Tuesday -- argued that Trump "remains open to change."
It's House Republican leadership, he said, who remain inflexible and have "dug their heels in."
"They are not going to compromise," he told CNN. "So the only way that we are going to get to a compromise where they listen to the grassroots that wants complete repeal, the only way we got to that compromise is that we have to demonstrate to the House leadership that we have the votes to stop them."
The President hits the road Wednesday night with a campaign-style rally in Nashville where he's expected to try to sell the bill.
Next week he's slated to do the same in Louisville. Asked how he feels about the president targeting Paul's home state of Kentucky, Paul said he's "happy to have him" and that he and the president agree on the "repeal part" of Obamacare, but they're "still apart somewhat on replacement."