Mark Udall, U.S. representative from Colorado and candidate for the U.S. senate, campaigns at a Fourth of July parade in Greeley, Colorado, U.S., on Friday, July 4, 2008.
Credit: Matthew Staver / Bloomberg / Getty Images

As we descend into the first creek valley, the trail becomes unclear in the gathering darkness. We arrive at a slope of untouched snow and pause. Beyond it stands an impenetrable-looking wall of trees. "Go for it," Udall says. "You're young."

"You first," I say. He pushes off, making one good telemark turn before falling sideways into the powder. As he struggles to his feet, kicking and sloughing off snow, he yells, "This is not a metaphor for the campaign!"

Perhaps a better campaign metaphor comes one Saturday in late August in the form of a chilly downpour soaking Denver and neighboring Littleton, where Udall was supposed to spend the morning at a parade. The Denver suburbs are crucial to Colorado elections, but there will be no campaigning in Littleton today. The good news is that the rain (and snow, at higher elevations) is dampening the lodgepoles in the mountains, staving off the danger of wildfire for the time being.

He's wearing the same blue Marmot jacket he wore the last time I saw him, which was in January. "This is my Denali jacket," he says proudly. In the madness of the campaign, even his Gore-Tex threatened to become an issue, as opponent Bob Schaffer suggested that maybe it was a little too fancy, a little too yuppie, a little too Boulder for the rest of the state. The attacks faded when it turned out that the jacket was made by Coloradans right there in Colorado. But still. It's been a rough few months.

Back in June, barely eight weeks earlier, Udall had a comfortable 10-point lead in the polls, with momentum going his way. The LCV was running hard-hitting TV ads tarring Schaffer, who has worked for a Denver energy company since leaving Congress in 2003, as "Big Oil Bob." The group also named Schaffer to its "Dirty Dozen" list of anti-environmental legislators. And Schaffer had been further embarrassed when the 'Denver Post' published photographs of him parasailing in the Mariana Islands on a 1999 trip that was financed by jailed lobbyist Jack Abramoff. In July, his 19-year-old son Justin's Facebook page came to light, featuring the slogan "Slavery gets shit done."

But then gas prices jumped, and suddenly being in the oil business didn't seem like such a terrible thing for Schaffer; at least he might know where to get some. Udall found himself stumbling over campaign trip wires on even his signature issues, and the polls showed the Republican closing the gap, almost to a dead heat. In a debate, Schaffer challenged Udall to pledge to vote against adjourning Congress so the House could finish an energy bill. Udall foolishly accepted, and he raced back to D.C. He was sprinting up the Capitol steps when the vote was called, to the delight of Schaffer's campaign manager, Dick Wadhams, who vowed to "shove a bunch of 30-second ads up his ass." The guy behind the Swift Boat ads four years ago piled on, giving $400,000 to the ultra-right-wing Club for Growth for ads assailing Udall's tax record.

The attacks seemed to work: In mid-August Udall suddenly reversed his longstanding opposition to offshore oil drilling, a sacred tenet of environmentalism since the Santa Barbara offshore oil spill of 1969. So did Nancy Pelosi, Barack Obama, and other Democratic leaders, but it was Mark Udall whom the 'Wall Street Journal' singled out by name in a blood-in-the-water lead editorial challenging the Democrats to make oil drilling (somehow) a plank of their party platform.

It was a long way from the relatively genteel environment Udall's dad had known in the 1960s and 1970s and even 1980s, when a liberal Democrat could befriend a guy like John McCain even though they disagreed on many if not most issues. Whereas Mo lived amid Washington's social whirl, the life of the party, Mark spends weeknights in a 400-square-foot apartment on Capitol Hill, then flies home to spend weekends with Maggie and their kids, now both in college. Family rules stipulate no events on Sundays.

But today is Saturday, and Udall is headed for yet another face-to-face debate with the sharp-tongued Schaffer, his third in three days, this one at a Catholic church in Colorado Springs – evangelical country. Today the subject is immigration, and the bumper stickers in the parking lot seem none too friendly. (I didn't know the John Birch Society still existed.) The Springs is home to the U.S. Air Force Academy, and, predictably, Schaffer tries to body-slam Udall on the "Department of Peace" thing.

Afterward, as Udall wedges his lanky frame into the campaign Prius, he's amped on adrenaline from the debate. He has the air of a man who can't wait for November, one way or the other. He'll either be headed for the Senate with his cousin Tom, or he'll have a lot more time to go climbing and contemplate the connection I ask him about now – between climbing a mountain and another long, slow, frustrating process: politics.

"The difference," he says once he has calmed down, "is that when you're climbing a political mountain, there's another team up there trying to push you off."