Senate Democrats facing tough elections this year want the Internal Revenue Service to play a more aggressive role in regulating outside groups expected to spend millions of dollars on their races.In the wake of the IRS targeting scandal, the Democrats are publicly prodding the agency instead of lobbying them directly. They are also careful to say the IRS should treat conservative and liberal groups equally, but they’re concerned about an impending tidal wave of attack ads funded by GOP-allied organizations. Much of the funding for those groups is secret, in contrast to the donations lawmakers collect, which must be reported publicly.One of the most powerful groups is Americans for Prosperity, funded by the billionaire industrialists Charles and David Koch. It has already spent close to $30 million on ads attacking Democrats this election cycle.“If they’re claiming the tax relief, the tax benefit to be a nonprofit for social relief or social justice, then that’s what they should be doing,” said Sen. Mark Begich (D), who faces a competitive race in Alaska. “If it’s to give them cover so they can do political activity, that’s abusing the tax code. And either side.”Asked if the IRS should play a more active role policing political advocacy by groups that claim to be focused on social welfare, Sen. Jeanne Shaheen (D-N.H.) responded, “Absolutely.”“Both on the left and the right,” she said. “As taxpayers, we should not be providing a write-off to groups to do political activity, and that’s exactly what we’re doing.”She called the glut of political spending by self-described social welfare groups that qualify under section 501(c)(4) of the tax code “outrageous.”Shaheen is in a good position now but could find herself embroiled in a tight campaign if former Sen. Scott Brown (R-Mass.) challenges her.Sen. Mark Pryor (Ark.), the most vulnerable Democratic incumbent, said the IRS has jurisdiction over 501(c)(4) groups, as well as charities, which fall under section 501(c)(3) of the tax code and sometimes engage in quasi-political activity.