2004
In 2004, Udall announced his candidacy for the Senate seat which was being vacated by Ben Nighthorse Campbell.
However, the following day, Colorado Attorney General Ken Salazar announced his candidacy as well.
Udall bowed out of the race and endorsed Salazar.

2008
On January 15, 2007, incumbent Senator Wayne Allard announced he would not run for a third term.
In April 2007, Udall announced his campaign for the Senate.
Udall became the Democratic nominee for the race after running unopposed in the primary.
In the general election, Udall faced former U.S. Representative Republican Bob Schaffer.
By August 28, 2008, over $10 million had been spent on attack ads against Udall by political parties and political action committees, an amount higher than in any other Senate race that year.

The race was especially competitive, with Democrats wanting to expand their majority as much as possible due to that year's presidential election.
While both CQ Politics and The Rothenberg Political Report estimated Udall would win, and The Cook Political Report considered it a 'Toss Up,' Udall maintained a steady lead in the polls, but with neither candidate usually topping 50%.
Udall described the race as "the toughest climb I've ever taken."
On November 4, Udall won the election with 52% of the vote.

2014
On January 7, 2013, Udall announced he was running for re-election.
Udall was unopposed in the Democratic primary, and faced Republican U.S. Representative Cory Gardner in the general election.
 Although Udall was heavily favored in early polls, around September, Gardner gained and held a steady lead thereafter.

Udall's re-election campaign focused on reproductive and women's rights.
Throughout, Udall attacked Gardner for his former support of a fetal personhood initiative, and claimed in ads that Gardner "championed an eight-year crusade to outlaw birth control here in Colorado."
PolitiFact.com rated his claim "half-true," saying that it "leaves out important details."
On MSNBC's The Last Word, Alex Wagner attributed Udall's trailing poll numbers to his "focus on reproductive rights."
 Due to his campaign's emphasis on these issues, Udall was ridiculed as "Mark Uterus."
In an October 2014 Denver Post endorsement of his opponent, the editorial board stated that "Udall's campaign has devoted a shocking amount of energy and money trying to convince voters that Gardner seeks to outlaw birth control despite the congressman's call for over-the-counter sales of contraceptives.
Udall is trying to frighten voters rather than inspire them with a hopeful vision."

Towards the end of his campaign, Udall was accompanied by Second Lady of the United States Jill Biden, Massachusetts Senator Elizabeth Warren, and former Secretary of State Hillary Clinton.
In July 2014, President Barack Obama headlined a fundraiser for Udall's campaign.
2004
In 2004, Udall announced his candidacy for the Senate seat which was being vacated by Ben Nighthorse Campbell. However, the following day, Colorado Attorney General Ken Salazar announced his candidacy as well. Udall bowed out of the race and endorsed Salazar.
2008
On January 15, 2007, incumbent Senator Wayne Allard announced he would not run for a third term. In April 2007, Udall announced his campaign for the Senate. Udall became the Democratic nominee for the race after running unopposed in the primary. In the general election, Udall faced former U.S. Representative Republican Bob Schaffer. By August 28, 2008, over $10 million had been spent on attack ads against Udall by political parties and political action committees, an amount higher than in any other Senate race that year.
The race was especially competitive, with Democrats wanting to expand their majority as much as possible due to that year's presidential election. While both CQ Politics and The Rothenberg Political Report estimated Udall would win, and The Cook Political Report considered it a 'Toss Up,' Udall maintained a steady lead in the polls, but with neither candidate usually topping 50%. Udall described the race as "the toughest climb I've ever taken." On November 4, Udall won the election with 52% of the vote.
2014
On January 7, 2013, Udall announced he was running for re-election. Udall was unopposed in the Democratic primary, and faced Republican U.S. Representative Cory Gardner in the general election.  Although Udall was heavily favored in early polls, around September, Gardner gained and held a steady lead thereafter.
Udall's re-election campaign focused on reproductive and women's rights. Throughout, Udall attacked Gardner for his former support of a fetal personhood initiative, and claimed in ads that Gardner "championed an eight-year crusade to outlaw birth control here in Colorado." PolitiFact.com rated his claim "half-true," saying that it "leaves out important details." On MSNBC's The Last Word, Alex Wagner attributed Udall's trailing poll numbers to his "focus on reproductive rights."  Due to his campaign's emphasis on these issues, Udall was ridiculed as "Mark Uterus." In an October 2014 Denver Post endorsement of his opponent, the editorial board stated that "Udall's campaign has devoted a shocking amount of energy and money trying to convince voters that Gardner seeks to outlaw birth control despite the congressman's call for over-the-counter sales of contraceptives. Udall is trying to frighten voters rather than inspire them with a hopeful vision."
Towards the end of his campaign, Udall was accompanied by Second Lady of the United States Jill Biden, Massachusetts Senator Elizabeth Warren, and former Secretary of State Hillary Clinton. In July 2014, President Barack Obama headlined a fundraiser for Udall's campaign.
Mark Udall