WASHINGTON — As presidential candidates find new ways to exploit secret donations from tax-exempt groups, hobbled regulators at the Internal Revenue Service appear certain to delay trying to curb widespread abuses at nonprofits until after the 2016 election.

In a shift from past elections, at least eight Republican presidential candidates, including leading contenders like Jeb Bush and Senator Marco Rubio of Florida, have aligned with nonprofit groups set up to raise hundreds of millions of dollars. Hillary Rodham Clinton’s supporters are considering a similar tactic.

Some of these so-called social welfare nonprofit groups are already planning political initiatives, including a $1 million advertising campaign about Iran by a tax-exempt group supporting Mr. Rubio.

The groups are able to carry out many of the same political activities as candidates and their affiliated “super PACs” but do not have to disclose where they get their money, allowing total anonymity for donors.