Mr. Johnson shares some of the cross-party appeal of Representative Ron Paul of Texas, who complimented him publicly last week. Advisers said Mr. Johnson’s potential for cutting into Mr. Romney’s support was greatest in Florida, where Mr. Romney is basically tied with Mr. Obama, but could also have an impact in Arizona, Nevada, New Hampshire and North Carolina.
They said Mr. Johnson’s potential to eat into Mr. Obama’s support was greatest in Colorado, Iowa, New Mexico, Oregon and Wisconsin.
Republican officials have already tried to challenge Mr. Johnson’s place on the ballot or are trying to in states including Iowa, Michigan, Ohio, Pennsylvania and Virginia. Many of the challenges have failed — courts recently rejected efforts to throw him off the ballot in Virginia — and Roger Stone, a Republican Party veteran who is advising Mr. Johnson, said he was optimistic that Mr. Johnson would qualify in all 50 states.