In November, Coffman defeated Joe Miklosi, a former state representative, by just two points (or roughly 7,000 votes out almost 343,000 cast).

The Cook Political Report, an online election handicapper, ranks the contest as among the most competitive of the 2014 cycle, with the advantage currently leaning toward Coffman.

Romanoff is no stranger to national elections, having vied to replace former Sen. Ken Salazar (D-Colo.) in 2010 after President Obama tapped Salazar to head the Interior Department. Romanoff lost that bid, defeated by now-Sen. Michael BennetMichael Farrand BennetOvernight Finance: Trump wants Russia back in G-7 | Senators, allies push back | House approves first fiscal 2019 spending bills | Dems want insider trading probe over job tweet Dems want insider trading probe after Trump jobs report tweet Clinton on his reading habits: 'I like a fast ride' MORE in the Democratic primary.

Pelosi's visit to Denver is part of a broader tour through the West. 

On Tuesday, she was in Albuquerque, N.M., with Rep. Michelle Lujan Grisham (D-N.M), where the pair was joined by women's rights advocates to promote the Democrats' campaign for gender equality in the workplace.

Wednesday evening, she'll host a fundraiser for Rep. Jared Polis (Colo.), a three-term Democrat representing the Boulder area.