To understand why Sen. Lamar Alexander decided to leave the Republican leadership on Tuesday, look no further than his parking spot on Capitol Hill, where he keeps his Nissan Leaf, a plug-in electric car that most conservatives would dismiss as a Liberal-mobile.

Alexander gleefully defends his Leaf as the only choice a freedom-loving American would make. “Plugging in my Nissan Leaf will give me the patriotic pleasure of not sending money overseas to people who are trying to blow us up,” he said when he picked up the keys to his new ride in May.

All of this is to say that Lamar Alexander, a conservative by almost any measure who ran for the GOP presidential nomination in 1996 and 2000, is not like the others in the Senate Republican leadership.

While Alexander has a history of working where he can to find common ground with Democrats on issues from clean air to education, Mitch McConnell has declared it his goal for the 112th Congress to make Barack Obama a one-term president. As the Republican caucus in the Senate has grown more conservative with the addition of Tea Party firebrands like Rand Paul and Pat Toomey, Alexander has had to abandon his bipartisan ambitions to keep his seat at the leadership table.

On Tuesday, the former Tennessee governor and Education secretary under George H.W. Bush reversed course and announced that he will leave his post as the third-ranking Republican in the Senate, a decision that shocked people, if only for its sheer novelty. When was the last time someone in Washington volunteered for less power instead of more?

But the practical considerations behind Alexander’s decision make perfect sense for a man who has long led a double life as both a devoted institutionalist in the Senate, where consensus is the only path to progress, and a Republican Party loyalist fighting to take back the Senate and advance the party platform. The balance, Senate staffers say, has been tough for Alexander, who has led efforts among his colleagues to strike bipartisan deals, only to be told by McConnell to dial it back and make room for the party line.

Alexander said that leaving the leadership and returning to the rank and file will liberate him from one role to concentrate on the other on Tuesday.

“For four years my job on the Republican leadership team has been to help the leader and individual senators succeed,” he said on the Senate floor. “There are different ways to offer leadership within the Senate.”

But he was also quick to stress that leaving his post does not mean he is leaving the Republican Party or considering retirement at the end of his current term in 2014.

“I am a very Republican Republican,” he said.  “I intend to be more, not less, in the thick of resolving serious issues.”

What Alexander did not mention in his floor speech was the difficult path he may have faced next year if he had stayed in the leadership and run for the No. 2 spot being vacated by retiring Sen. Jon Kyl.

Alexander said that leaving the leadership and returning to the rank and file will liberate him.

Although Alexander is well-liked in the caucus and has long-time friendships with senators, including McConnell, he would have had to face off against Sen. John Cornyn, the affable and very conservative Texan who is poised to help the GOP win back the Senate majority in 2012 and return their entire caucus back to their spots as committee chairmen and poobahs of their state delegations.

Some Republicans say Alexander could have held his own in the face-off, but his colleagues gave him a standing ovation at their private lunch Tuesday, partially to thank him for sparing them all the fight.

In the end, the 71-year old Alexander may actually wield more power, not less, as a freelancer in the Senate, at liberty to do deals with Democrats instead of as a marginalized member of his party’s lock-stepping leadership. With major battles brewing over spending, entitlement reform, taxes, and deficits, both parties will now have to fight for Alexander’s vote and, in some cases, craft their proposals with his position in mind.

Don’t mistake Alexander’s readiness to make a deal with his willingness to become a squish, especially going into a reelection cycle to hold onto his Senate seat.  Alexander continues to hammer the president’s record on health-care reform and financial reform as “more government takeovers,” and generally derides Obama’s birdshot approach to leading the country.

But the Tennessean is still enough of a throwback to call hardline Democrats “rascals,” and to see the value in working with the rascals if he can get to yes and solve a problem he wants dealt with.  Jim Jeffries, Alexander’s spokesman, says he’ll focus his efforts on energy, education, advanced research, and growing the economy.

Dr. Bruce Oppenheimer, a political science professor at Vanderbilt University in Nashville, says that Alexander’s announcement Tuesday will give him the flexibility to break from the party where he sees fit, a luxury he has not had for years.

“To be in the leadership, there is a price to pay within the party, given his conservative, but not extreme conservative, positions on a range of issues," Oppenheimer says.  "He may not be willing to pay that anymore.”