WASHINGTON — Growing Republican dominance of Senate seats in states where George W. Bush has run best looms as the principal obstacle for Democrats hoping to retake the chamber in 2006 or beyond.
With the recent struggle over judicial nominations underscoring the stakes, the battle for Senate control could attract unprecedented levels of money and energy next year.
Democrats are optimistic about their chances of ousting GOP senators in Pennsylvania and Rhode Island, states that voted for Democratic presidential candidates John F. Kerry in 2004 and Al Gore in 2000. But the Democrats are unlikely to regain a Senate majority -- in 2006 or soon thereafter -- unless they can reverse the GOP consolidation of Senate seats in states that have supported Bush.
Since 2000, both parties have gained Senate seats in the states they typically carry in presidential campaigns. But this political partitioning provides a clear advantage for Republicans because so many more states backed Bush in his bids for the presidency.
If Democrats only gain in their part of the map, "it's like saying, 'We're going to win more home games but never worry about road games,' " said Matthew Dowd, a political advisor to the Republican National Committee and senior strategist for Bush's reelection campaign. "They could have a great home record but never win a majority."
Republicans control 55 Senate seats and Democrats 44, with Vermont independent James M. Jeffords holding the final spot. In next year's midterm election, Republicans will defend 15 seats and Democrats 17. And Vermont voters will choose a successor to Jeffords, who is retiring.
As the parties approach these contests, the political divide familiar from presidential campaigns figures ever more prominently in their calculations.
Twenty-nine states voted for Bush in 2000 and in 2004. Republicans now hold 44 of the 58 Senate seats in those so-called red states. That's a much higher percentage of in-party Senate seats than Presidents Reagan and Clinton were able to claim in states they carried twice.
More important, on the strength of those states alone, the GOP is on the brink of a majority in the 100-member Senate.
Democrats are just as strong in the states that voted for Kerry and Gore. But there are only 18 of those so-called blue states; Democrats hold 28 of those 36 Senate seats.
Republicans also hold four of the Senate seats in the three states that switched parties from 2000 to 2004 -- New Mexico, New Hampshire and Iowa.
This distribution makes it virtually impossible for Democrats to regain a majority simply by defeating GOP senators from blue states, such as their two top targets for 2006 -- Rick Santorum in Pennsylvania and Lincoln Chafee in Rhode Island.
Whatever happens in those races, the Democrats' ability to win Republican-held Senate seats next year in red states such as Montana, Tennessee and Missouri -- and to defend their seats in red states such as Nebraska, Florida and North Dakota -- may reveal more about their long-term prospects of regaining a Senate majority.
Democratic pollster Geoff Garin noted that in the last two elections, Democrats have come close to taking the White House, even though they've lost more states than they've won. That's because the high-population states they did win -- such as New York and California -- have large numbers of electoral college votes. But, regardless of population, each state has two Senate seats, so Democrats must compete on a broader map to realistically contend for a Senate majority.
"You can cobble together a viable electoral college strategy with a minority of states, but you simply can't cobble together a Senate majority that way," Garin said.
As recently as the 1980s, it was common for states to split their ballots in presidential and Senate contests.
But the sharpening partisan edge of modern politics has made it tougher for senators to survive -- in effect, behind enemy lines -- in states that consistently prefer the other party in presidential campaigns.
The result has been a decline in the Southern Democrats, who bucked the region's growing preference for GOP presidential candidates, and in the Northeastern Republicans, who overcame their area's Democratic tide in national campaigns.
Forty-four states supported Ronald Reagan for president in 1980 and 1984. But partly because of lingering Democratic strength in the South, Republicans after 1984 controlled only 48 of the 88 Senate seats in those states, about 55%.
The trend toward consolidation gained momentum in the 1990s. Bill Clinton won 29 states twice. After his second victory, Democrats held 35 of the 58 Senate seats in those states, or 60%.
In the elections of 2000, 2002 and 2004, Republicans gained a net of six Senate seats in the red states that Bush carried twice. Democrats added four Senate seats in the blue states that twice voted against Bush; Republicans lost another blue-state Senate seat when Jeffords quit the GOP in 2001.