Federal Election Commission guidelines adopted in the wake of the Supreme Court decision prohibit independent groups from coordinating expenditures with their favored presidential candidates and limit how much candidates can directly help raise for the groups. And during Mr. Romney’s brief appearance before current and prospective donors to Restore Our Future, he made no appeal for money, according to participants.

Gail Gitcho, a Romney spokeswoman, declined to comment on the event, saying only that “any activity done by our campaign is done within the letter and the spirit of the law.”

In a statement, Jason Miller, a spokesman for Make Us Great Again, said the group would abide carefully by all federal restrictions.

“There is an absolute firewall between Make Us Great Again and the campaign, and there is no communication between the two regarding activities, plans or projects,” Mr. Miller said. “Everybody involved with our efforts, including Mike Toomey, is very careful about this.”

But some advocates for tighter campaign regulation say existing rules on independent groups did not anticipate the emergence of Super PACs so closely tied to a single candidate, leaving so much room to maneuver that the independent groups are able to act as surrogates for the candidates.

“There’s not a big difference between these candidate-specific Super PACs and candidate campaign committees,” said Paul S. Ryan, associate legal counsel at the Campaign Legal Center. “I think it’s a joke. What they are doing is abiding by the very meager restrictions on coordinations on expenditures and solicitations. But that leaves a wide swath of activities that can be fully coordinated under present law.”

Increasingly, the new Super PACs are taking on tasks that in previous years were handled by — and paid for — the candidates themselves. But instead of using money raised in the $2,500 increments that federal law imposes on candidates, the Super PACs can accept donations of unlimited amounts. (The groups must disclose their donors, though some Super PACs, including Priorities USA and the Karl Rove-founded American Crossroads, have affiliated nonprofit arms that do not have to disclose donors.)