Here are the 12 most important takeaways from National Journal's 2013 ratings:
1. It's hard to believe, but Congress is likely to be even more polarized next year.
Three of the five most moderate Democrats in the House—Jim Matheson of Utah, Mike McIntyre of North Carolina, and Bill Owens of New York—have already announced their retirements this year. John Barrow, the most moderate Democrat, faces another difficult reelection campaign in deeply conservative rural Georgia. In the Senate, it's plausible that as many as six of the 11 most moderate Democrats could be gone next year; some are retiring, some are facing tough reelection campaigns.
It's not much better for the remaining GOP centrists. Half of the 10 House Republicans who have announced their retirement—Frank Wolf in Virginia, Jim Gerlach in Pennsylvania, Jon Runyan in New Jersey, Spencer Bachus in Alabama, and Tom Latham in Iowa—rank in the top fifth of moderate Republicans.
2. Republican presidential candidates in Congress continue to showcase their conservatism.
Every prospective Republican presidential candidate ranked as reliably conservative, although none more so than Cruz in his first year on the job. He ranked as the fourth-most-conservative senator, with a composite score of 95.0, fully living up to his reputation. Cruz outdistanced Sen. Marco Rubio of Florida (tied for 17th) and Paul (19th) in that respect, but both of them ranked in the top half of conservative senators. (Paul's 82.0 composite conservative score was a slight drop-off from his 2012 rating of 90.8, when he ranked sixth in the Senate.)
Likewise, House Budget Committee Chairman Paul Ryan ranked as one of the most conservative representatives, with an 81.2 composite conservative score. That put him in the upper-third of House Republicans, ranking 71st. But Ryan opened himself up to conservative criticism late last year in negotiating a bipartisan budget deal that averted a government shutdown. In the Senate, 36 Republicans voted against the compromise, including Cruz, Rubio, and Paul.
3. Red-state Democrats are breaking with their party, but their Obamacare votes still lurk.
Democrats facing tough reelection campaigns in red states this year can point to evidence that they're more moderate than Republicans give them credit for. Of the 11 Democratic senators who rank as the most moderate, nearly half are facing the political fights of their careers. Leading the pack is Mark Pryor of Arkansas, who is the second-least-liberal senator, with a 46.2 composite score. Kay Hagan ranks as the fourth-least-liberal. Also at the top of the list are Alaska's Mark Begich (54.7 liberal), Virginia's Mark Warner (56.3 liberal), and Louisiana's Mary Landrieu (58.3 liberal).
It's worth noting that every Democratic senator, even West Virginia's Joe Manchin, is more liberal than the most moderate Republican senator, Maine's Susan Collins. That's both a result of congressional polarization and a sign of the Democratic Party's leftward drift. And all of the Democrats supported President Obama's health care law, their most politically consequential vote in recent years.