Mark Kirk, the Republican running in Illinois’ Senate race, became the first federal candidate to return donations from Goldman Sachs, in the wake of the SEC’s civil fraud lawsuit.

Congressman Mark Kirk, the Republican nominee for an open Senate seat in Illinois, said he will return contributions made by Goldman employees because the SEC is investigating the bank.

Kirk, 50, made the announcement after his Democratic opponent, Illinois Treasurer Alexi Giannoulias, criticized him for taking the donations. The two men are vying for the Senate seat once held by President Barack Obama that will help determine whether Democrats retain control of the chamber.

“We are calling on Congressman Kirk to explain why he voted against Wall Street reform,” said Matt McGrath, a spokesman for Giannoulias. “And we are challenging him to give back his tainted Goldman Sachs campaign contributions.”

Kirk has taken $54,010 from Goldman employees, including $21,600 for his Senate bid, McGrath said.

Kirk is particularly exposed here. He is basing much of his campaign on his opponent’s family ties to Broadway Bank, a failing financial institution in Illinois. It would smack of total hypocrisy for Kirk to dismiss the Goldman situation when he’s so exposed to it.

However, Blanche Lincoln, who also has been hammered by her opponent for ties to Wall Street, won’t join Kirk. She simply said “No” when asked if she would return Goldman contributions at a press event today. And she added, “I don’t think I’ve accepted contributions disproportionately from any group.”

Lincoln may feel her turn on derivatives, which probably won’t even hit the final bill, will inoculate her from criticism. I don’t think her primary opponent Bill Halter agrees.

UPDATE: Bill Halter’s communications director, Laura Chapin, responds:

Arkansans need no bigger example of the fact that Washington is broken than Sen. Lincoln’s refusal to return contributions from Goldman Sachs, a Wall Street firm that she voted to bail out and is now under federal indictment for fraud.

No, they’re not letting up.