I watch all 100 senators’ voting records very closely, and I’ve been surprised at just how obstinately conservative Sen. Mark Kirk of Illinois has been despite that fact that he’s incredibly vulnerable. On vote after vote where I expected him to break with the lunatics, he has gone right along with them. I figured he was first and foremost concerned with avoiding a primary loss. I guess I was wrong.

Sen. Mark Kirk, R-Ill., is ruling out campaigning for longshot GOP Illinois U.S. Senate nominee Jim Oberweis, saying Monday he would rather “protect” his relationship with Sen. Dick Durbin, D-Ill., and not launch a “partisan jihad.”

Kirk and Durbin are a very rare couple in Washington. They get along, even when they disagree. They grew closer after Kirk suffered a severe stroke, keeping him away from the Capitol for almost a year.

As a result, the two have forged for now an informal, unspoken, non-aggression pact.

Kirk’s more-than-kind words for Durbin will be very useful to Durbin in his race against Oberweis — where Durbin is the front-runner. A mutual disarming is potentially vastly more beneficial to Kirk, who already has said he will run for another term in 2016 and could potentially face a Democrat with some juice.

Durbin aside, it helps Kirk, a social moderate, who supports gay marriage, abortion rights and comprehensive immigration reform, to disassociate himself from Oberweis, who is opposite him on the very issues that may appeal to the swing independent suburban voters, especially suburban women who Kirk has cultivated throughout his congressional career.

Kirk commented after I asked him and Sen. John Cornyn, R-Texas — they were together in Chicago on Monday — if they would be seeing or campaigning for Oberweis.

“I’m going to be protecting my relationship with Dick and not launching into a partisan jihad that hurts our partnership to both pull together for Illinois,” Kirk replied.

Cornyn, a former chair of the National Republican Senatorial Committee — the Senate Republican political operation — sidestepped a question about helping raise money for Oberweis.

“The reason I am here is for my own re-election, so I’m not getting involved in the Illinois Senate race at this time,” Cornyn said.

Buddying up to Durbin might help Kirk win reelection in a general election, but it assures that the Republican base will treat him like we treated Lieberman. So, all those lunatic votes were for nothing.