Mitt Romney takes his fading case for the Republican presidential nomination to the heart and soul of the conservative base Thursday, making a longshot plea to the annual Conservative Political Action Conference in Washington, D.C.

Whatever case he makes, front-runner John McCain, buoyed by a growing legion of conservative backers, gets the last word as he follows Romney into the lion's den to convince activist conservatives he is one of them.

Romney is far behind McCain in the delegate count for the GOP nomination but conservative support seems to be coalescing around him. He has won the endorsements of conservative luminaries like talk show host Rush Limbaugh and former Pennsylvania Sen. Rick Santorum, and is hoping a strong message to CPAC will push the audience to do his bidding ahead of upcoming contests.

The CPAC event in Washington, D.C., is well-timed. Next week is the Potomac Primary -- the Virginia, Maryland and Washington, D.C., contests -- and Romney is stuffing his visit to the area with another event -- a Thursday evening Lincoln Day Dinner in Baltimore that was pushed up on the calendar to precede Tuesday's primary.After his visit to the mid-Atlantic region, Romney will also be campaigning in Kansas and Washington state, which hold Republican caucuses on Saturday, and Ohio and Texas, which have primaries on Feb. 19. Romney has generally done best in caucuses states.

While Romney is addressing a friendly crowd -- a CPAC straw poll taken at last year's conference put him first in a list of potential '08 nominees --the former Massachusetts governor's toughest challenge is closing the widening gap in delegates pledged to the candidates ahead of September's Republican National Convention.

McCain has 703 delegates to Romney's 293, according to the latest Associated Press count, and the Arizona senator's campaign points out that Romney would have to win almost all the remaining 963 delegates in states yet to vote to win the nomination.

That challenge appears even more formidable looking at current polling data. In Maryland, a Baltimore Sun poll taken last week gave McCain a double-digit lead over opponents Mike Huckabee and Romney. An average of national polling done by RealClearPolitics also gives McCain a more than 18-point lead over Romney.

Still, McCain, who has traditionally skipped the big CPAC event, can't afford to stay away this year. Last year, McCain placed fifth in the CPAC straw poll, behind Romney, Sam Brownback, Rudy Giuliani and Newt Gingrich. Brownback and Giuliani are now out of the race and supporting McCain, but the conservative chorus against him has grown stronger since he began collecting victories in the 2008 Republican presidential primaries.

But McCain, known for his independent streak, could still sell his conservative credentials, which include hawkish national security positions, a 100 percent anti-abortion record, appointing constitutionalist judges to the bench and fiscal discipline.

"I have a long conservative record," McCain said in Phoenix as he basked in his Super Tuesday successes while trying to impress his record on conservative voters.

"We share the common principles and values and ideas for the future of this country based on a fundamental conservative political philosophy, which has been my record," McCain said.