An early resignation by Sen. Thad Cochran, R-Miss., for health reasons, something aides and allies insist is not imminent, could set up another front in the civil war that threatens to roil Republican primaries in 2018.

Insurgents preparing to challenge Sen. Roger Wicker, R-Miss., next year are now eyeing the special election that would be called if Cochran stepped down. It's a concern for a Republican establishment faced with diverting resources from the general election to quash a rebellion initiated by Steve Bannon, President Trump's former chief strategist.

Cochran's office in Washington maintains that there is no cause for alarm about the senator's health, although the 79-year-old is being treated for unspecified "urological issues" and remains under medical supervision and aides concede that his work schedule could be impacted. This comes after a three-week absence from the Senate to allow for recovery.

"The fact of the matter is, he has been struggling for a long time, and everything is not hunky dory," a worried Republican insider said, on condition of anonymity in order to speak candidly.

"I think he's going to be just fine," Wicker countered, although he conceded that, at that point on Wednesday afternoon, he had yet to see or talk to Cochran. Of the resignation rumors, Wicker added: "There's nothing to that at all."

Republicans fretting about Cochran's health, and the political implications of his possible resignation, appeared to have their anxiety validated later in the day. According to Politico, the senator appeared disoriented and confused on his way the Senate floor on Wednesday to cast key votes on the budget.

Losing Cochran's virtually guaranteed "yes" vote on forthcoming tax reform legislation could be a big blow to President Trump and Senate Majority Leader Mitch McConnell, R-Ky. Passage of the bill rests on a thin GOP majority. "His health is a concern," a Republican lobbyist monitoring the tax negotiations said.

It's another headache for top Republicans in Mississippi and Washington as they game out the electoral implications of Cochran resigning before his seventh term ends in 2020.

Republican Gov. Phil Bryant would have 10 days to appoint a replacement, to serve until a nonpartisan special election was held to determine a permanent successor. If Cochran resigned before Nov. 6, the day of next year's midterms, the special would occur in 90 days. Most likely low turnout, an insurgent would have the advantage.

If Cochran resigned after Nov. 6, the nonpartisan special would be held the same day as the 2018 midterm, when Wicker also is on the ballot. The appointee would serve until then, and presumably have a leg up on the competition assuming this individual ran.

Rep. Gregg Harper, R-Miss., who is close with Bryant, could receive the appointment. So could Lt. Gov. Tate Reeves. Bryant could face pressure from the Right over the selection.

"Phil Bryant's entire legacy as governor hinges on the adroitness with which he can select a replacement for Thad Cochran, who is clearly less than capable of serving the people of Mississippi by adequately performing his senatorial duties," said Noel Fritsch, a GOP operative who advises outsider candidates and served as the spokesman for Cochran's 2014 primary challenger, Chris McDaniel.

An extra Senate race in Mississippi, a solid red state, provides the anti-establishment wing of the GOP another opportunity to challenge for a Republican Senate seat and oust McConnell from leadership, their primary goal. Bannon is leading the charge here, raising resources and recruiting candidates to take on incumbent GOP senators and undermine the majority leader.

McDaniel, who narrowly lost to Cochran in GOP primary runoff three years ago, is being courted by Bannon to challenge Wicker. The senator votes with Trump more than 95 percent of the time, but he's a McConnell loyalist. McDaniel would happily oppose the majority leader, a proud, driving force behind his narrow loss to Cochran in the 2014 primary.

McDaniel said that he hopes to make a decision about 2018 by month's end. He said that Cochran's situation had no bearing on his plans. McDaniel had some choice words for Wicker, accusing him of obstructing Trump's agenda because he opposes discarding the supermajority filibuster for legislation. But he declined to criticize Cochran.

"My only prayer is that right now Sen. Cochran recovers fully. We have significant differences, but I want to see him recover. I want to see him happy, I want to see him healthy," McDaniel said.