Sen. John McCain (Ariz.) will test his appeal among Republicans in states across the country Tuesday, but a tougher sell awaits him two days later in Washington when he makes his pitch to a hostile group of stalwart conservatives he spurned last year.

McCain will speak to the Conservative Political Action Conference (CPAC) annual convention Thursday at 3 p.m., two and a half hours after Mitt Romney, his chief rival for the nomination and the preferred conservative choice, addresses the crowd.

The dynamic changed, however, after McCain beat Romney in last week’s Florida primary despite being vastly outspent. One day later, McCain accepted CPAC’s longstanding invitation to speak at its convention, and started trying to pull the fractured party together again with pledges to appoint conservative judges and ads stressing his support for lower taxes. But he still has a lot of persuading to do.

“Sen. McCain is a very smart guy and I’m sure he knows he needs the support of the conservative movement if he’s going to win the election this fall,” said Pat Toomey, president of the fiscally conservative Club for Growth.

Sponsored by organizations such as the American Conservative Union, Judicial Watch and Concerned Women for America, the CPAC convention attracts grassroots activists from across the social and fiscal conservative wings of the party.

In addition to talking taxes and economic theory, McCain will have the opportunity to reach out to those on the religious right, who haven’t forgotten how he lashed out at Pat Robertson and Jerry Falwell on the eve of the 2000 Virginia primary.

In 2004, Christian evangelicals were credited with giving President Bush the final push over the finish line to win, but this year they could stay home in large numbers if McCain fails to energize them. In contrast, the Democratic base is electrified with record turnout at the primary polls, outnumbering Republicans by a rate of 7 to 5 before Florida, where Democratic delegates didn’t count.

“My hope would be that there’s a way to come to terms, but it’s not clear to me how that happens,” said Toomey, who repeatedly noted that he did not think it is a forgone conclusion that McCain, well ahead of Romney in some national polls, will become the GOP nominee.

McCain took a shot at the Club early last year, saying he didn’t know what he had in common with the group. The Club responded by distributing a video to its members and the press of a McCain appearance on CBS’s “Face the Nation,” in which McCain explained why he didn’t support the “last round” of the Bush tax cuts. McCain explained that the tax cuts were too focused on nation’s wealthiest citizens.