By Gabriel Debenedetti
WASHINGTON (Reuters) - Groups aligned with the Tea Party movement are targeting two Republican U.S. senators who backed a bipartisan budget plan on Thursday, vowing to support their challengers in Republican primaries before congressional elections in 2014.
The plan to reopen the federal government and increase the nation's borrowing authority ended a 16-day government shutdown that conservatives backed in an unsuccessful attempt to weaken Democratic President Barack Obama's healthcare overhaul.
Hours after Congress passed the measure, the Club for Growth and the Senate Conservatives Fund endorsed Chris McDaniel, the Tea Party Republican from Mississippi who is running for the seat occupied by Senator Thad Cochran.
"Chris McDaniel is a constitutional conservative who will fight to stop Obamacare, balance the budget, and get America working again, the Senate Conservatives Fund statement said.
Cochran was among 27 Senate Republicans to support the plan to end the shutdown. Senate Minority Leader Mitch McConnell, a Kentucky Republican who helped to craft the deal, faced a similar backlash on Friday.
McConnell's primary opponent, Tea Party candidate Matt Bevin, was endorsed by the Senate Conservatives Fund, a group founded by former South Carolina Senator Jim DeMint, a leading voice of the Tea Party.
The movement swept a wave of right wing lawmakers to Capitol Hill in 2010 and helped Republicans regain the House of Representatives. Groups like Club for Growth donated heavily to a slate of successful candidates during that election cycle.
Club for Growth - whose influence over dozens of the most conservative members of Congress is such that its pronouncements have effectively killed some budget proposals - already had targeted Republican Representative Mike Simpson, the only one of Idaho's four members of Congress to vote for the bill that ended the shutdown.
Club for Growth is backing Tea Party Republican Bryan Smith as a more conservative alternative to Simpson. Smith also has been endorsed by FreedomWorks, a conservative group whose chief executive, Matt Kibbe, predicted on Friday that Tea Party conservatives' frustration with moderate Republicans could lead a split of the Republican Party.
Taken together, the endorsements signal that the battle over Obamacare - and far-right conservatives' push to put more of their candidates in Congress with an eye toward killing the Affordable Care Act - is far from over.
Club for Growth and the Senate Conservatives Fund are major contributors to the campaigns of several staunch conservatives. The Center for Responsive Politics says they are the two largest donors to Senator Ted Cruz, the Texas Republican whose 21-hour floor speech in September helped set the stage for the shutdown fight over the health reform law.
Cochran, 75, has been in office since 1978 and has not officially announced that he is running for re-election in 2014.
In endorsing McDaniel, Club for Growth's political action committee (PAC) said in a statement, "If Cochran runs for re-election, he will likely have the entire Republican establishment behind him - all the more reason that Senator McDaniel will need the strong support of the Club's PAC."
McConnell, who has been in office since 1984 and has clashed with Cruz, will face a two-pronged challenge next year.
Well-funded Democrat Alison Lundergan Grimes, Kentucky's secretary of state, is running for McConnell's seat. But before he can face her, McConnell has to defeat Bevin in the Republican primary.
In backing Bevin, the Senate Conservatives Fund cited various votes by McConnell to fund the government, which the group equated to funding Obama's health care law.
McConnell's campaign mocked the SCF's endorsement of Bevin.
"Matt Bevin now has the dubious honor of standing with a self-serving D.C. fundraising group that made its name by recruiting and promoting unelectable candidates that ensured Barack Obama a majority in the Senate," McConnell spokeswoman Allison Moore said in a statement.
"They clearly care less about Kentuckians than they do about their reputation for supporting laughably bad candidates," Moore added.
DeMint, the Senate Conservative Fund's founder, emphasized the ongoing efforts to pressure moderate Republicans on Friday with an editorial in the Wall Street Journal headlined, "We Won't Back Down on Obamacare."
In an interview on Thursday, Club for Growth president Chris Chocola, a former Indiana congressman, pledged to endorse more candidates, noting that the shutdown and surrounding debates "may have defined our opportunities a little bit better."
Heritage Action spokesman Dan Holler also said his group would keep fighting the health reform law, in part by helping the opponents of Democrats in conservative states, such as Senators Mark Pryor of Arkansas and Kay Hagan of North Carolina.
(Editing by David Lindsey and Doina Chiacu)