CQPolitics.com’s first roundup of the 2008 Senate races — with earliest-ever Election Forecaster ratings by the CQPolitics staff — is based on this increasingly irrefutable principle: the concept of the “off-election” year is now an anachronism for Senate incumbents and candidates.

These ratings come with a major caveat: Much will change in many of these races in the more than 21 months before Election Day 2008. And many of these ratings will change — some drastically — over that long stretch.

The ratings chart below highlights one of the biggest challenges facing the Republicans: Of the 34 seats up for election next year, 22 are currently held by Republicans and only 12 are being defended by the Democrats.