Rep. Cory Gardner speaks at a political rally in Littleton, Colo. (AP Photo/Brennan Linsley)

For weeks, Rep. Cory Gardner (R) and Sen. Mark Udall (D) have been statistically tied in polls of the Colorado Senate race, with Gardner in the lead but well within the margin of error. Now a new poll, taken over the last four days, shows Gardner leading by seven points.

According to the USA Today/Suffolk University poll, Gardner is at 46 percent to Udall's 39 percent. A September poll from the same pollster had Gardner up by just one, 43-42. Both polls have a margin of error of plus or minus 4.4 percent, meaning neither shows Gardner with what can technically be considered a firm lead. But seven points is his biggest edge since an outlier poll last month showed him up by eight points.

I reached out to David Paleologos, the director of the Suffolk University Political Research Center, to ask him about the state of the race and what has changed since September:

"It's not all Udall's fault; it's an anti-Washington D.C. feeling. But it's not hurting Gardner as much," he said. "The other part is that local news that took place in Colorado over the weekend about the teenagers trying to enlist in (the Islamic State) and they lived in Denver suburbs. That was a huge Colorado news story, and I think a lot of people were immediately tuned in. Voting is emotional, and when you have high anxiety it gets picked up in the polling. It could settle down."

Paleologos also said that Udall, who has been campaigning heavily on women's issues, has lost his edge with women over the last month. "It's close among women, and we don't know whether that is security or ISIS issues or parents of children or other issues," he said.

One poll in and of itself, of course, isn't the whole ballgame. But 10 of the last 11 independent public polls have shown Gardner in front, and Democrats are starting to worry about this one getting away from them. Udall's camp remains confident, but others are becoming very worried that a race that wasn't really on the radar at the start of 2014 now favors the GOP.

As a result of the new poll, a state that Obama won twice is now in USA Today's "lean Republican" column. Our Election Lab forecast model gives Gardner an 87 percent chance of flipping the seat. Both are, it's worth noting, among the most bullish projections of Gardner's chances.

Democrats have taken an all-in approach to this race, with Hillary Clinton and Sen. Elizabeth Warren (D-Mass.) visiting in the final days trying to rally the base. It has become quite clear that it will be very difficult for Democrats to hold the Senate without Colorado, which makes this one very important.

Colorado is also a state in which voters can mail in a ballot, and that process is well underway. On that score, Republicans are in the lead. But Democrats hope that the increased turnout that accompanies mail-in ballots will help them by getting casual voters to cast ballots.

Udall's campaign has and continues to insist that its ground game will make all the difference and that the only poll that matters is the one on Election Day. But, the trend line in the race doesn't look good for him.

Update 5:48 p.m.: DSCC executive director Guy Cecil, a veteran of Sen. Michael Bennet's (D-Colo.) 2010 campaign in Colorado, tweets the following in response to our story:

Cecil is kind of right. Per Real Clear Politics, only one of the final 18 polls in Colorado in 2010 showed the eventual winner, Bennet, with a lead. But two others showed it tied. So technically the Republican led in 15 out of 18 polls.

Every poll in the final three weeks of the campaign showed Republican Ken Buck between a tie and a four-point lead. Bennet won by less than a point.