By claiming “social welfare” status (which it clearly does not deserve), the group can keep the identity of its donors secret from voters. The Rubio people are not alone in adopting this strategy: Vital election and tax laws are being increasingly circumvented, as campaign strategists in both parties game the system with a message of catch-me-when-you-can. The Democrats worked from the social welfare shadows last year in campaigning for the Senate, collecting half of the $30 million in “dark money” raised by the group Patriot Majority USA from just five anonymous donors, according to the Center for Public Integrity watchdog group.

Image Marco Rubio. Credit... Charles Krupa/Associated Press

Meanwhile, regulators at the Internal Revenue Service and the notoriously toothless Federal Election Commission are looking the other way.

In the case of Conservative Solutions, the group has not bothered to seek advance approval from the Internal Revenue Service for its “social welfare” claim, leaving its status to be officially settled, if ever, sometime well after the presidential election, when few will care.

Even so, two watchdog groups, Democracy 21 and the Campaign Legal Center, have called on the tax division of the Justice Department to investigate the dodgy operation now for what it is, an obvious political initiative that should be subject to disclosure. It violates the law, the groups complained, by providing a private benefit for a partisan campaign, featuring Mr. Rubio and nobody else in thousands of television ads in the early primary states of Iowa, New Hampshire and South Carolina, all paid by the Conservative Solutions Project.

As he campaigns, Mr. Rubio is offering voters proper-sounding prescriptions about the growing problem of secretive funds. “As long as you know who’s behind the money and how much they’re giving and where they’re spending it, I think that’s the sunlight that we need,” he told a New Hampshire voter earlier this year.