Bob Schaffer’s campaign for Colorado’s open U.S. Senate seat got both good news and bad news Tuesday.

So, first the good news: A new Rasmussen Reports poll released this afternoon put Schaffer’s opponent ahead by four points, 47 percent to 43 percent. The good news is that’s five points less than lead for Democrat Mark Udall that Rasmussen’s tracking survey showed a month ago.

Because a series of polls have all recently shown Udall with at least a nine point lead (the latest was a survey by Public Policy Polling released just a week ago), there is a question about what’s occurred in the last few weeks to explain the shift, especially Udall’s drop with independent voters (from a 21 point advantage in the Rasmussen survey a month ago to just four points today). One factor could be the limited reliability of the poll itself. Rasmussen uses robo-calls that lead respondents automatically through a series of questions, a cost-effective method that several political experts have questioned as unreliable (the poll has a margin of error of 4.5 percent). But another could be the issue of gas prices. Schaffer had consistently painted Udall in the last few weeks as a pro-environmental candidate who has helped block more domestic drilling in the Alaska National Wildlife Refuge (ANWR) as well as off America’s coasts, and that may have hit home with voters angry about the cost of filling up their tanks.

The bad news for Schaffer is that Congressional Quarterly moved the state’s Senate race from “a toss up” to “leans Democrat” in its highly respected tracking of contested races. The publication cites Udall’s lead in fundraising, a national headwind for Democrats, and previous polls that showed the Democrat’s increasing lead. The race, CQ says, is now Udall’s to lose. Other publications, including the non-partisan Cook Political Report, traditionally one of the most accurate of the political trackers, keeps the race as a toss-up, suggesting among other things that it’s too early to take much heed of the poll numbers.

Given the recent big swings in the Rasmussen survey, the Cook Report might just be right.