Now that Joseph Lieberman can see the end of his days in the U.S. Senate, many are examining one of the more fascinating careers of the last few decades of American politics.

Lieberman certainly has his critics — on all sides. Most of the Connecticut senator's critics come from the left, a political agenda he embraced early in his career, but an area that he moved away from in the last decade. Supporters call him independent and free-thinking, while others characterize him as a flip-flopper. The latter is hard to ignore, considering he was Al Gore's running mate in 2000, yet he endorsed his friend, Sen. John McCain (R-Ariz.), for president in 2008. But when it comes to environmental policy, Lieberman's allegiances are consistent.

Back in 1990, before his love affair with McCain and his flirtation with the vice presidency, Lieberman was an original sponsor of the landmark Clean Air Act. A year later, he introduced a bill that called for banning hazardous pesticides that consumers had been exposed to for decades. After introducing the bill, Lieberman said the EPA didn't have enough teeth to protect consumers from the dangers of such chemicals: "We have found that it often takes EPA 15 to 20 years to remove a dangerous pesticide from the market."

Years later, the then-junior senator made several attempts to amend a bill sponsored by Sen. Fred Thompson (R-Tenn.) and Sen. Carl Levin (D-Mich.). Those amendments called for an increase in the EPA's ability to conduct "risk assessments" relating to toxic air pollutants. The removal of such assessments in the Clean Air Act weakened that law, according to Lieberman. Despite his claims that his amendment would fix those shortcomings, Lieberman's amendment failed along party lines — with the exception of then-Republican Sen. Arlen Specter of Pennsylvania.

When it came to global warming, Lieberman has remained a pro-science and pro-facts member of the Senate. He co-wrote an editorial with McCain about the need to address global warming. Lieberman was a "yes" vote on the bill to ban drilling in the Arctic National Wildlife Refuge in Alaska. When Republicans moved to reduce oil usage by 5 percent by 2025, Lieberman said the number should be 40 percent. When running for president, Lieberman said in a debate at Pace University that he favored raising the U.S. mileage standard in automobiles to 40 miles per gallon.

Like most eco-minded people, Lieberman was a critic of the Bush administration's environmental policies, or lack thereof. He voted against the appointment of scandal-ridden Gale Norton to the position of Interior secretary. Lieberman did, however, vote for the Energy Policy Act of 2005, which was a gift to polluters and the fossil fuel industry.

Yet three years later, Lieberman joined forces with Sen. John Warner (R-Va.), back when Republicans and Democrats tried to do things together. The Lieberman-Warner Climate Security Act of 2008 was the cap-and-trade bill, but it failed. Two years later, Lieberman joined forces with Sen. John Kerry (D-Mass.) for another cap-and-trade bill, but with tensions high in the Senate and the difficulty of corralling Sen. Lindsey Graham (R-S.C.), the bill never had a chance.

The environment is an interesting legacy for Lieberman; it's one with few blemishes. Lieberman certainly has an odd reputation: he's a senator who could work with Democrats and Republicans but who could be equally difficult for both parties to deal with at times. He has also been even harder to defeat — just ask Ned Lamont.

Over the next two years there will be discussion about whom Lieberman worked with and whom he worked against, but it's clear that almost every time he could, he worked to protect the environment.

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Lieberman's environmental legacy
Often criticized by members of both parties, Sen. Joseph Lieberman has been a staunch supporter of the environment throughout his career.