Cousins Tom and Mark, whose fathers were leading liberals in decades past, each won Senate seats, a 'return to our roots' in the interior West.

Brothers Mo and Stewart -- Morris K. Udall was a congressman from Arizona who sought the 1976 Democratic presidential nomination, and Stewart L. Udall was a celebrated secretary of the Interior under Presidents Kennedy and Johnson -- fought for the environment and workers' rights. By the time they left politics in the 1980s, the interior West, the mountainous states east of California, had become a Republican stronghold.

On Tuesday, however, Mo's and Stewart's sons won U.S. Senate seats in New Mexico and Colorado, while the Democratic presidential candidate scored decisive wins in three of the most populous states in the region.

"It's back to our future; it's a return to our roots in the West," Rep. Mark Udall said in an interview last week after he won Colorado's Senate seat, which is currently held by a Republican.

Democrats for decades have dreamed of transforming the interior West into a place where the Udalls' politics could upend the GOP's electoral dominance.

On Tuesday, the party picked up the two Udall seats in the Senate and six House seats in the region, nearly one-third of their gains nationwide. Democratic governors represent the states running from Montana to Arizona. New Mexico's congressional delegation, for the first time in decades, will be entirely Democratic.

And Barack Obama -- whose presidential campaign poured resources into the region -- won Colorado, Nevada and New Mexico by convincing margins. The first two states had backed George W. Bush in both of his campaigns; New Mexico went for Bush by a slim margin in 2004 after Al Gore narrowly won it in 2000.

"Every two years, you're seeing more and more Democratic gains in the West," said Jill Hanauer, president of Project New West, which advises Democrats on how to expand in the region. "This could be for Democrats what the South was in the 1960s."

There are several factors at play: An influx of people from the more-liberal coasts has helped the party, as has a surge in Latino immigrants, who increasingly are voting Democratic.

On Tuesday, Obama carried two-thirds of the Latino vote nationwide, according to exit polls. In the West, where Republicans have pushed policies to crack down against illegal immigration, the margins were higher. In Nevada, 78% of Latinos backed Obama.