Republican centrist senators who have participated in negotiations on crafting a bipartisan healthcare bill have been among those targeted and pressured by political and business interests during the August recess, Sen. Max BaucusMax Sieben BaucusBooker tries to find the right laneĀ  Top Lobbyists 2017: Hired Guns GOP tries to keep spotlight on taxes amid Mueller charges MORE (D-Mont.) claimed Friday.

Baucus, the chairman of the Senate Finance Committee and leader of the so-called "group of six" senators negotiating a reform bill, said that the three Republican members of that group have been under tremendous pressure from their own party.

"The Republican leadership in the Senate and in the House is doing its utmost to kill this bill," Baucus told the editorial board of the Helena Independent Record. "They are putting intense political pressure on Chuck GrassleyCharles (Chuck) Ernest GrassleyFBI informant gathered years of evidence on Russian push for US nuclear fuel deals, including Uranium One, memos show Klobuchar taking over Franken's sexual assault bill Lawyer: Kushner is 'the hero' in campaign emails regarding Russia MORE, Olympia Snow and Mike EnziMichael (Mike) Bradley EnziGOP senators ask Trump for meeting on biofuels mandate Senate budget just the latest attack on seniors Week ahead: GOP's next steps on tax reform | Fed chief speculation heats up | Senate to vote on disaster relief MORE, to bow out, because they want to kill it."

Baucus pointed specifically to the prospects of his committee's ranking member, Sen. Grassley, potentially facing a primary challenge next year over his work on the healthcare bill.

"He knows a lot of the opposition against him is orchestrated," he said. "I don't know this, but I strongly suspect they're going to Iowa, they're trying to stir things up to get somebody to run against Chuck in the primary."

Baucus said he doesn't believe that Grassley would abandon the negotiations, but offered words of sympathy for the Iowa Republican and the other two senators working on putting together a bill.

"I know it's easy for me to say right now, because I'm getting beat up by both sides, but not nearly as much as you are by the Republican hierarchy," he said.