WASHINGTON (AP) — Ron Paul, the congressman from Texas and a favorite of tea partyers, effectively ended his presidential campaign Monday but urged his fervent supporters to continue working at the state party level to cause havoc for presumptive Republican nominee Mitt Romney.

 In an email to supporters, Paul urged his libertarian-leaning backers to remain involved in politics and champion his causes despite the apparent end of his presidential aspirations. Paul has found success in wrecking the selection process for delegates to the party's late-summer nominating convention in Tampa, Fla., and trumpeted that he has delayed Romney's expected nomination.

"Moving forward, however, we will no longer spend resources campaigning in primaries in states that have not yet voted," Paul said in his statement. "Doing so with any hope of success would take many tens of millions of dollars we simply do not have. I encourage all supporters of liberty to make sure you get to the polls and make your voices heard, particularly in the local, state and congressional elections, where so many defenders of freedom are fighting and need your support."

 Paul's supporters have proved successful in winning state GOP conventions in places such as Maine and Nevada. His supporters in Iowa and Nevada were chosen to lead the state central parties.

 Paul's flock is likely to make similar inroads this weekend in Minnesota, which Paul was slated to address. Paul has already dominated the state's congressional district conventions, winning at least 18 of the 24 national delegates selected, even though he finished a distant second to Rick Santorum in local caucuses in February.

 "Our campaign will continue to work in the state convention process. We will continue to take leadership positions, win delegates and carry a strong message to the Republican National Convention that liberty is the way of the future," Paul vowed.

 Primaries have not been Paul's strong suit — he hasn't won a single primary or caucus. But Paul's supporters have successfully navigated the convention process in a number of states, adding to Paul's delegate total while gaining influence over state parties.

 Romney, however, is on pace to capture the nomination this month. He has 973 of the 1,144 delegates required to formally become the GOP's nominee, according to an Associated Press tally. Vanquished foe Santorum has 264 and Newt Gingrich has 130. Paul badly trails with 104 delegates.

 Romney already is campaigning against Obama, and Paul's announcement does little to change the head-to-head campaign in November.

 Paul is unlikely to endorse Romney as the party's nominee. The pair strongly clashed during the debates over foreign policy, and in interviews Paul has refused to say he would champion Romney's campaign.

 Many of Paul's libertarian views dovetail nicely with mainstream Republican ideas on limited government and low taxes. But Paul breaks with much of his party when he rails against American intervention abroad and government efforts to fight terrorism at home — positions that earned him a loyal following.

Paul, a longtime congressman, is not running for another term to represent his Texas district.

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(Photo: AP Photo/Ben Margot, File)