Congratulations to President Obama and to Supreme Court Justice Sonia Sotomayor.

Obama made a historic pick and stood by her, and Sotomayor will bring great distinction and -- yes -- empathy to the Court.

Now the question is, who's next?

It seems likely that Justice John Paul Stevens and Justice Ruth Bader Ginsberg will step down before Obama's term is over.

I'd like to suggest that the President nominate Sen. Russ Feingold to fill the next spot.

Feingold has the intellectual heft for the job, as he was a Rhodes Scholar and then graduated from Harvard Law School.

He is one of the staunchest defenders of civil liberties in the country, and he chairs the Senate Judiciary Subcommittee on the Constitution. Not afraid to stand alone, he was the sole Senator to vote against the USA Patriot Act. He also has led the fight against illegal domestic spying, and he has spoken out strongly against the shredding of due process in the Military Commissions Act.

Here's why Feingold should be attractive to Obama.

During the presidential campaign, Obama recognized the benefits of nominating someone who has held political office. Asked at a town hall meeting in Westerville, Ohio, on March 3, 2008, about whether he would return to that earlier presidential practice of nominating political figures as opposed to simply picking from people on the lower courts, Obama responded: "I think you're absolutely right."

"Some of our best justices," he added, have come not from the lower courts, but from "people who know a little about how the world works and who know what it looks like outside of a courtroom."

Historically, almost one out of every four justices had previously served in Congress. Five were incumbent Senators, including Hugo Black. But since Black retired in 1971, no one from Congress has made it up to the high court.

On the campaign trail, Obama also said, in his interview with the Rev. Rick Warren, that he wanted someone on the Supreme Court who would guard against expansive Presidential powers. Here was Obama's answer to Warren's question about why he didn't vote for Chief Justice Roberts: "One of the most important jobs of the Supreme Court is to guard against the encroachments of the Executive Branch on the power of the other branches."

There is no one in the country who guards against those encroachments with more backbone than Russ Feingold.

Two other practical considerations are in Feingold's favor.

First, he's only 56 and seems in very good health and could likely serve on the Court for decades.

Second, and more importantly, he may very well be the most progressive confirmable person Obama could choose for this spot.

Feingold has made a habit of working across the aisle, as evidenced by the McCain-Feingold campaign reform law, as well as his work on the Honest Leadership and Open Government Act and his fiscal hawkishness. It would be very difficult for his Republican colleagues to deny him a seat on the highest court.

Would Feingold be interested in being on the Supreme Court? I asked him once, and the idea seemed to entice him.

Obama would do himself proud, and his progressive base proud, and the Constitution proud, by nominating Russ Feingold to fill the next vacancy on the Supreme Court.

