The Potomac poll estimated one-sixth of the voters in the Republican primary will be independents, though there are more than one-third as many registered independents as Republicans.
Caliguiri said that the McCain campaign plans mailings to all the state's independent voters before the primary.
Bush supporter McCabe said McCain's appeal to independents -- and Democrats in states where they can vote in Republican primaries -- is often at the expense of his own party.
"It bothers me to see someone trying to get the Republican nomination by running against the Republican Party," he said.
Ironically, the move to open the Maryland primary to independents, passed at the state Republican convention last year, was backed by those who now support Bush and opposed by many who back McCain.
"I think it was Ellen Sauerbrey's and Dick Bennett's idea," said Caliguiri, referring to state party Chairman Richard D. Bennett, who is on the ballot as a Bush delegate.
"But I do think it fits in well with McCain's message of opening up the party to all kinds of folks," Caliguiri said. "This is the vote we are going to compete for in the general election. If a candidate can't win those votes now, he's not going to be as strong in November."
Sun staff writer John Rivera contributed to this article.