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Former Denver Mayor Frederico Pena: Getty Images PhotoDENVER - Frederico Pena, Former Secretary of Energy and former Mayor of Denver, speaks during day two of the Democratic National Convention (DNC) at the Pepsi Center August 26, 2008 in Denver, Colorado. U.S. Sen. Barack Obama (D-IL) will be officially be nominated as the Democratic candidate for U.S. president on the last day of the four-day convention. (Photo by Win McNamee/Getty Images)

U.S. Rep. Chris Van Hollen (D-Md.), the chair of the Democratic Congressional Campaign Committee, appeared onstage at the party's national convention in Denver Tuesday, bringing eight Congressional hopefuls along with him.

Van Hollen said it wasn't enough for Democrats to elect U.S. Sen. Barack Obama (D-Ill.) to the White House; they had to expand their majority in Congress, he said. 

Among those Democratic challengers who appeared with Van Hollen was Jared Polis, who is seeking Colorado's 2nd Congressional District seat, which is being vacated by U.S. Rep. Mark Udall.

The results of a survey released Tuesday by polling firm Rasmussen Reports showed U.S. Sen. Barack Obama (D-Ill.) with a slight lead over U.S. Sen. John McCain (R-Ariz.) in the race for Colorado's presidential endorsement.

The poll showed presumptive Democratic presidential nominee Obama with 49 percent support, while his Republican counterpart McCain garnered 42 percent. The 4.5-point margin of error suggested the race could be tighter than the numbers indicate, however, and with so-called leaners included, Obama's lead shrank to three percentage points.

The results come one day after polling firm Zogby International released even closer poll results. Zogby gave Obama a two-point lead, well within the 3.6-point margin of error.

A Rasmussen poll in June showed Obama with a 43-41 lead over McCain; in May it was 48-42 for Obama.

A Democratic victroy in Colorado would be historic. The state has gone to the Democrats just once in the last 40 years, when Bill Clinton defeated George H.W. Bush in 1992.