Environmental groups used to like Republican U.S. Rep. Mark Kirk.
They picked him over a Democrat in two heated congressional races and he cited their support in countless ads, crafting an image as an independent politician.
"We are extremely disappointed ... and we want the people of Illinois to know that," says Tony Massaro, League of Conservation Voters senior vice president for political affairs.
Kirk, now a candidate for U.S. Senate, just signed a pledge from a conservative group opposing President Barack Obama's push for cap-and-trade legislation aimed at taxing pollution tied to global warming.
It's the same legislation that Kirk voted for earlier this year while in the U.S. House, and he was singled out by conservative groups and commentators as one of only eight Republicans to support the Democratic proposal.
Kirk says he voted for it then because his North suburban 10th District supported it. He argued it was also a matter of national security as an important element of weening America off foreign oil.
But soon after declaring his candidacy for Senate, Kirk started saying he would oppose the measure if elected to represent Illinois in the upper chamber of Congress. Now he says the southern Illinois coal industry would be hurt by the legislation and it would be irresponsible of him to support it.
Critics have deemed Kirk's move a transparent attempt to pacify opponents in the more conservative base of the party as he works through a GOP primary fight for the Senate seat.
Powerful national conservative groups have been eyeing Patrick Hughes of Hinsdale to possibly support, but they have yet to pull the trigger less than two months from the Feb. 2 primary.
Kirk spokesman Eric Elk said Friday the five-term congressman has a long history of supporting environmental policies, including moves to clean up the Great Lakes and prevent pollution increases. Elk says opposing cap-and-trade shouldn't label Kirk as anti-environment.
"Congressman Kirk will continue to support policies that end our dependence on foreign oil and improve our environment without harming Illinois jobs and incomes," Elk said.
Yet, environmental groups have been an important element of support Kirk has used to gain traction beyond Republican voters, backing that he may well need to win a statewide Senate race next year.
Kirk has also relied on endorsements from gun control advocates and legalized abortion supporters to strengthen his image as a "moderate."
Environmental groups who champion cap-and-trade say Kirk has now cost himself general election support in a decidedly Democratic state. Cap-and-trade tops their agenda and appears to surpass other pro-environment positions the congressman holds.
"Mark Kirk is catering to a very vocal, very angry minority," says Jack Darin, director of the Sierra Club's Illinois chapter. "This is a very important seat and we want to know that our next U.S. senator is going to be a leader on environmental and energy policy."
Both the Sierra Club and League of Conservation Voters sided with Kirk in his 2008 race against Wilmette Democrat Dan Seals, a battle that drew millions of dollars in spending and national attention.
Both groups have yet to endorse in the Republican Senate primary, though it is unlikely they will find a candidate to back who supports cap-and-trade in the current field.
An endorsement from the Sierra Club or League of Conservation Voters often carries more than just kind words to put on campaign mailers and TV ads.
Just this summer the League of Conservation Voters paid for cable TV ads in Illinois urging Kirk to continue supporting cap-and-trade.
Massaro pointed out the organization played a significant roll for Barack Obama in his 2004 Senate primary bid. The group bought $400,000 in TV ads for Obama early in the Democratic race.
"We will be doing more than just the general work for whoever we pick in Illinois," Massaro said of the upcoming general election.
But what he has lost in support from environment groups, Kirk may have gained from the so-called right.
Joe Calomino, Illinois director for Americans for Prosperity, said Kirk was right to sign his organization's pledge against cap-and-trade.
"I think our members were outraged, clearly," Calomino says, "and we are grateful he changed his mind."
Other candidates in the GOP primary for Senate include Internet commentator Andy Martin of Chicago, retired judge Don Lowery of downstate Golconda, Springfield activist Kathleen Thomas, former Harvey alderman John Harrington and Rockford businessman Robert Zadek.