Even before yesterday’s Florida win, John McCain was racking up endorsements from conservative Republicans such as Senator Martinez of Florida and Jack Kemp, a former congressmen from New York.

But other conservatives have their doubts. On Monday, the president of the Leadership Institute, Morton Blackwell, was quoted in the Chicago Tribune saying: “I think Senator McCain is essentially hostile to the conservative base of the Republican Party and he is wrong on many, many issues that are important to the conservative base.”

Tom Delay, the former House majority leader, said on January 17, “If McCain gets the nomination, I don’t know what I’ll do. I might have to sit this one out.”

Who’s right? Does the Arizona Senator qualify as a solid conservative? Or does he lack persuasive credentials?

For voters who seek a conservative, the question now boils down to this: Is Mr. McCain less conservative than Mitt Romney, the other leading contender?

Mr. McCain’s rise has paralleled the success of the military surge in Iraq, which he championed before President Bush. The senator served in the Navy between 1958 and 1981, including stints as a combat aviator in Vietnam and a prisoner of war for five and a half years. Governor Romney did not serve.

But he has made many enemies in Washington because he’s not afraid to speak his mind, often bluntly, whether mocking Senate colleagues for their pet porky projects, or saying that undocumented workers are “God’s children.” Mr. McCain is no diplomat.

Mr. McCain’s lifetime rating from Americans for Tax Reform, a group dedicated to lower taxes, is 83 out of 100, similar to that of Fred Thompson, a favorite of conservatives who quit the race last week and whose rating is 84.

Notwithstanding those numbers, one of conservatives’ biggest gripes against Mr. McCain is that he did not vote for President Bush’s tax cuts, citing deficit concerns. People therefore say that he is not a committed tax-cutter.

On the other hand, he has never voted for tax increases. Mr. McCain has led the fight for a moratorium on keeping the Internet untaxed. His tax plan calls for making President Bush’s tax cuts permanent, fully repealing the alternative minimum tax, and increasing business deductions.

Mr. McCain has consistently opposed earmarks and needless spending, the other side of the fiscal coin. He voted against the 2003 Medicare Modernization Act because it expanded the reach of government, whereas Mr. Romney extended the role of government in health care in Massachusetts. Mr. McCain was the only candidate courageous enough to campaign against ethanol subsidies in Iowa.

He has always been pro-life, unlike Mr. Romney, yet some Republicans complain that as senator he has not pushed a conservative social agenda. Most conservatives agree that abortion and marriage are clearly issues that can be left to states, and many have advocated a more limited role of the federal government with greater power to states.

Republicans rightly complain that the McCain-Feingold campaign finance reform bill of 2002, which limited the ability of individuals to contribute to candidates, violates Americans’ constitutional rights to freedom of speech, including campaign contributions, a form of political speech. Mr. Romney, though, supported public funding of campaigns in Massachusetts, either from state revenues or from a 10% tax on political contributions, as well as spending limits.

The deepest, most emotion-laden split among Republicans is on immigration. Mr. McCain proposed that undocumented workers who were in America before January 1, 2007 would be given a visa that would allow those without criminal records to apply for permanent residency after paying fines.

Mr. Romney now labels Mr. McCain’s proposals as “amnesty,” even though in an interview in November 2005 with the Boston Globe he said this of Mr. McCain’s immigration policy: “That’s very different than amnesty, where you literally say, ‘OK, everybody here gets to stay.’ It’s saying you could work your way into becoming a legal resident of the country by working here without taking benefits and then applying and then paying a fine.”

The conservative “solution” to illegal immigration is to build a wall along the Mexican border, deport undocumented workers when they are arrested for some other violation, and conduct routine sweeps of workplaces that might illegally employ immigrants.

This brings up the question of electibility. The Republican primary winner will have to command votes not only from Republicans but also from centrist Democrats and Independents. Much Republican discussion on immigration has been phrased in xenophobic language that has been interpreted as “Send All Foreigners Home.” This language frightens tens of millions of Americans, who might vote Democratic in reaction.

Mr. McCain is not the perfect candidate, but he embodies traditional Republican principles of smaller government and a strong defense. He has broad appeal to different groups. His documented inability to get along with the Washington establishment might even win him votes in a year when people are calling for change.