Sen. Menendez raises questions about legitimacy of 501 (c) (4) groups U.S. Sen. Robert Menendez, D-N.J., on Capitol Hill in Washington, Feb. 13, 2013. WASHINGTON, May 19 (UPI) -- A top U.S. Senate Democrat said Congress should expand its focus on the Internal Revenue Service and examine the use of non-profit groups for partisan purposes. In an appearance on ABC's "This Week," Sen. Robert Menendez, D-N.J., said Sunday conservative groups seeking tax-exempt status invited scrutiny because they were playing an increasing role in national partisan political strategies. Menendez said it was wrong for the IRS to single out conservative groups applying for tax-exemptions but he said the uproar in Washington over the tactic opened the door to broader questions about the activities of organizations seeking 501 (c) (4) tax status. "There's a second scandal, and that is that hundreds of millions of dollars had been used in C-4s that are supposed to be used a non-profit social welfare entities, for political purposes," Menendez said. It is pretty outrageous that the IRS went after small Tea Party groups when Karl Rove is out there saying he's using these C-4s to change the outcome of the next election. Sen. Rob Portman, R-Ohio, said on the same program the investigation should focus on what IRS employees did and whether the White House influenced the practice. "We can talk about whether the laws ought to be changed, and I am for tax reform," Portman said. But the question is whether there was an unbiased, even-handed enforcement of the laws.