One of the top election forecasters moved Colorado’s U.S. Senate election from the category of “toss up” to “leans Democratic” on Thursday.

Larry Sabato’s Crystal Ball, a nonpartisan project of the University of Virginia’s Center for Politics, cited Colorado voters’ continued preference for Democrats and incumbent U.S. Sen. Cory Gardner’s general support for President Donald Trump as reasons for the change. Gardner and Trump will rally together in Colorado Springs later on Thursday.

“This reelection path for Gardner isn’t impossible, but he needs some things to break his way in order to retain his seat. Hence, it makes more sense to look at Gardner as an underdog,” the Crystal Ball concluded.

The forecast noted that Gardner’s 48%-46% victory in 2014 over then-U.S. Sen. Mark Udall came in part from a strong performance in Congressional District 6. Since then, the district has voted in much greater margins for Democrats. The Crystal Ball concluded that Gardner would not likely receive many votes from Democrats in the district this time, “at least not in the necessary volume he’d traditionally need.”

Republicans currently control the U.S. Senate by a majority of 53-47. In the same update, the Crystal Ball moved its prediction for the seat of U.S. Sen. Doug Jones, D-Ala., to “likely Republican.”

One of the other main election forecasting groups, the Cook Political Report, retained Colorado’s Senate ranking as a “toss-up.”

The Democratic Party of Colorado on Thursday pointed to a poll from The Rocky Mountaineer, a progressive research group, showing that 37% of all voters approve of Gardner’s job performance, less than the 44% who approve of Trump. Among “very conservative Republicans,” 99% approved of Trump, compared to 76% who approved of Gardner.

The online survey consisted of 818 registered Colorado voters chosen at random and from those who opted in. The research group attempted to match the composition of the survey sample with the demographics of registered voters statewide. The survey took place from Jan. 31 to Feb. 4.