Conservatives candidates tend to stay conservative in office and progressives stick to their beliefs, too. Moderates pretty much stay moderate.
But last week, we witnessed the exclamation point of a pretty radical shift when U.S. Senator Mark Kirk (R-IL) cast the deciding vote to gut a critical climate measure.
It's not surprising that this Congress, with its open hostility to putting limits on carbon pollution, would attempt to derail the U.S. Environmental Protection Agency's Clean Power Plan. The shocking part is that the matter was decided, for now at least, by someone who ran for the Senate as an environmental moderate.
The committee vote is not the last word on the EPA's plan; hopefully the full Senate will reject this attempt to let the carbon spew. But it is certainly true that those who voted for this provision meant to put an end to the Clean Power Plan.
They are now on the record as favoring the status quo of unlimited carbon pollution from existing power plants -- the largest source of this pollution. Never mind the urgent need to reduce climate pollution, the asthma attacks and health costs that would be reduced, or the boost the plan would give to clean energy.
Back in 2010 when then-Congressman Mark Kirk ran for the Senate, there was reason to believe he would be a thoughtful moderate on environmental issues. In the House, he cast pro-environment votes about two-thirds of the time, according to the League of Conservation Voters.
But after his narrow win -- earned because he did better than other Republicans in independent and progressive areas of Illinois -- his record got worse. A lot worse.
During his time in the Senate, Kirk has cast anti-environment votes more than two-thirds of the time. You read that right: It's been a complete turnaround from two-thirds pro-environment to two-thirds anti-environment.
I can imagine that leaves a lot of moderate voters in Illinois feeling they got the bait and switch.
Kirk's lunge to the right was a genuine surprise to those who followed his pre-Senate career.
Maybe he changed his views to curry favor with party bosses in Washington. Maybe it was out of fear of the Tea Party. Or maybe his earlier pro-environment record was just an unavoidable necessity in his moderate House district.
But Democracy has a way of working these things. Kirk won by a small margin in a progressive state in a low turnout mid-term election.
Next year he has to run for re-election in that same progressive state in a high turnout presidential election year. Which means that next fall, lots of Illinois voters will get the chance to express their opinion on Senator Kirk's vote for unlimited carbon pollution.
Let's hope, for his sake, he cleans up his act before then.
This post originally appeared on EDF Voices