....

As the Democratic Party shifts leftward without much resistance, Republicans are fighting a war for the soul of their party. House Speaker John Boehner faces constant revolt on his right flank from a growing number of Tea Party-affiliated members who believe compromise is a dirty word. Outside conservative groups, such as the Club for Growth and the Senate Conservatives Fund, are enforcing ideological purity among members as well as primary candidates. Six of the 12 Republican senators up for reelection in 2014 are facing primary challenges from their right, even though several rank among the most conservative, according to the vote ratings.

....

Beyond the polarization, the vote ratings highlight other compelling findings. Among Republican presidential candidates, Texas's Ted Cruz proved he could vote more conservatively than Kentucky's Rand Paul, 2013's Tea Party favorite. Senator Elizabeth Warren of Massachusetts is not quite as progressive as she advertised, at least compared with her Democratic colleagues. While most Democratic senators have moved to the middle as they face competitive elections, Al Franken has remained a stalwart liberal. Meanwhile, John McCain and Orrin Hatch, who had moved to the right in preparation for primary races, once again occupy the moderate wing of the Republican Party. Contrary to conventional wisdom, most members whose districts became safer during the redistricting process didn't become any more ideological.

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.
2. Republican presidential candidates in Congress continue to showcase their conservatism.
3. Red-state Democrats are breaking with their party, but their Obamacare votes still lurk.
4. The Tea Party is running out of conservatives to target.
5. Conservatives will have reason to be steamed (again) at John McCain and Orrin Hatch.
6. Al Franken wears his liberal brand proudly, even when facing reelection.
7. Liz Cheney would never have had a shot against Michael Enzi.
8. Elizabeth Warren: Not as progressive as advertised?
9. The most liberal Democrats in the Senate are among the most hawkish on Iran sanctions.
10. Very few of the most conservative House Republicans face any serious Democratic opposition.
11. The oddest couple in the Senate: Wisconsin's Ron Johnson and Tammy Baldwin.
12. Most members who benefited from redistricting didn't change their voting patterns.

The Atlantic