(CNN) -- Republican presidential candidate Ron Paul is hinting that his run for the White House is about to end, saying the "presidential campaign will soon wind down."
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Rep. Ron Paul (R-Texas) ran for president as a Libertarian in 1988.

His comments came two days after Sen. John McCain became the presumptive GOP nominee.

"Though victory in the conventional political sense is not available in the presidential race, many victories have been achieved due to your hard work and enthusiasm," the Texas congressman said in a video to supporters posted by his campaign on YouTube on Thursday.

Former Arkansas Gov. Mike Huckabee announced Tuesday he was quitting the the Republican presidential race after McCain's victories in Tuesday's primaries, leaving Paul as his only opponent.

Paul, who ran for president as a Libertarian in 1988, is the sole Republican candidate to call for a U.S. withdrawal from Iraq. He is a distant fourth in the GOP delegate count, behind McCain, Huckabee and former Massachusetts Gov. Mitt Romney.

"We must remember, elections are short-term efforts," Paul said. "Revolutions are long-term projects."

Paul's "Hope for America" campaign has been a grassroots effort, focusing on a "limited constitutional government, low taxes, free markets, and a return to sound monetary policies," according to his Web site.

"But even with the past year's achievements, we're still the early stages of bringing about the changes that this revolution is all about."