UPDATED: 

A new survey from a Democratic polling firm released Monday provides further evidence that Democratic U.S. Senate candidate Mark Udall's once-substantial lead is continuing to slip.

The Public Policy Polling survey still showed Udall leading by 6 points. But  Republican U.S. Senate candidate Bob Schaffer gained three percentage points over July's PPP survey; Udall remained at 47 percent.

Other polls also show Udall's lead -- once in hovering near double-digits -- slipping in recent weeks; observers say high gas prices, among other issues, is helping Republican U.S. Senate candidate Bob Schaffer.

Monday's poll also showed Democrat Barack Obama with a 4-point lead over Republican John McCain in the U.S. presidential race in Colorado. That's the same lead Obama had in July's PPP survey.

The survey showed Obama with a 51-36 lead among Colorado Hispanic voters. McCain led among white voters 48-46. Obama is leading 50-35 among independents, the poll found.

Looking forward to the 2010 U.S. Senate race, incumbent U.S. Sen. Ken Salazar (D-Denver) leads U.S. Rep. Tom Tancredo (R-Littleton) and Secretary of State Mike Coffman 49-37 and 46-38, respectively.

The survey, conducted among 933 likely voters between Aug. 5 and Aug. 7, has a margin of error of +/- 3.2 percent.

EDITOR'S NOTE: The original post miscalculated the difference between Udall's lead in the the PPP's July and August polls. The difference is six percentage points.