Editor's note: Ruben Navarrette Jr. is a CNN.com contributor, a nationally syndicated columnist and an NPR commentator.
San Diego, California (CNN) -- Say it ain't so, Joe. But it is so.
Sen. Joe Lieberman announced Wednesday that he would not seek re-election. And, the Senate, the country and the political process are worse off for it.
Lieberman told reporters: "I've loved serving in the Senate and I feel good about what I've accomplished. But I know that it is the right decision, and I must say, having made it, I am excited to begin a new chapter of life with new opportunities."
The Connecticut lawmaker's biggest accomplishment in the Senate didn't come from passing a valuable piece of legislation or enriching the public debate with silvery oratory. Rather, his most important and lasting contribution was standing up to the extremes, staking out the middle ground and then successfully defending it when those on the left tried to topple him.
He taught Americans the value of following your heart and standing up for your ideals, even when they're not popular in your neighborhood, group or political party.
Let's remember that while Lieberman was once among the most popular elected officials in liberal Connecticut and nearly became vice president under the Democratic banner in 2000, he was always out of step with liberal orthodoxy.
In the 1990s, when the discussion in the Senate turned to school vouchers, affirmative action and privatizing Social Security, Lieberman cast votes and took positions that leaned to the right.
Also, it obviously didn't win him any support in the Democratic Party when, in 1998, he condemned President Bill Clinton's reprehensible behavior in the Monica Lewinsky scandal.
Tension builds. And eventually, Lieberman was run out of his party by intolerant liberal hardliners upset over his support for the Iraq War. The left had a lot riding on its anti-war message, after all. It was busy trying to use the war to bludgeon its nemesis: George W. Bush. And there was Lieberman, as they saw it, offering aid and comfort to the enemy.
He lost the Democratic primary, but he ran as an independent and retained his seat by drawing on Republican support.
For Lieberman, an Orthodox Jew, the issue in the Middle East was always more complicated than who was president. A staunch ally of Israel, Lieberman was dedicated to removing Saddam Hussein from power and bringing freedom and democracy to the Iraqi people, both of which would remove a dagger pointed at the heart of Israel.
He lost the last of his friends on the left when, in 2008, he spoke at the Republican National Convention and endorsed Republican John McCain, a longtime friend and ally, over Democratic nominee Barack Obama.
Still, in the Senate, Lieberman usually voted with Democrats. But this was not a foregone conclusion. On foreign affairs and military policy, he often voted with Republicans.
During his remarks to reporters, Lieberman acknowledged that he made plenty of enemies over the years on the way to becoming the middle-of-the-roader that liberals love to hate.
"I have not always fit comfortably into conventional political boxes," he said. "Maybe you've noticed that. Democrat, Republican, liberal or conservative. Because I've always thought my first responsibility is not to serve a political party but to serve my constituents, my state and my country."
Imagine. Here you had a lawmaker who was unpredictable and brave enough to take nuanced positions on complicated issues.
Don't we want more of that in our politics? Don't we need more? When did independence go out of style and even become, in some cases, a political liability? It used to be that conservative Democrats and liberal Republicans were the most interesting people in Washington. Now they're all but extinct.
We have a system that is rotten from the roots.
It starts with the redistricting process, where state lawmakers who aspire to become federal lawmakers cut their own districts and choose their voters instead of the other way around. The result is that we end up with very liberal members of Congress, seated right next to very conservative ones. Then, when anyone begins to think for himself, party leaders put a stop to that by pulling rank and punishing the dissenter.
It is little wonder that the political discourse is increasingly "all or nothing," and that it is getting harder and harder to find diverse views in either camp.
Joe Lieberman was different. He wasn't afraid to go his own way if he thought it was the right way. And he'll be missed.
Thanks for your career of public service, senator, and for being your own person. No doubt, one made the other worthwhile.
The opinions expressed in this commentary are solely those of Ruben Navarrette.