Dianne Feinstein, who has represented California in the U.S. Senate since 1992, isn’t going to have the smooth re-election process she might have hoped for. Reports are surfacing that Kevin de Leon, a fellow Democrat and the president of the California state senate, will challenge her in the state’s primary, and Feinstein might have reason to be worried.

As we’ve noted recently, the idea that Feinstein would face a primary challenge isn’t a total shock. During the first year of the Trump administration, Feinstein has been singled out by her liberal constituents for being too conservative for their taste. She’s been booed by them at town hall events and a late March poll of California adults showed that Feinstein’s approval rating had slipped 7 percentage points from the previous year, to 49 percent.

Feinstein is feeling the heat in part because her more liberal constituents are correct in surmising that she is more conservative — relative to the politics of the state she represents — than other Democrats. Feinstein has voted in support of President Trump’s agenda 31 percent of the time, according to our Trump score. Ten Democrats have voted with Trump more. But because California is so liberal — Trump lost there by 30 percentage points in 2016 — we’d expect Feinstein to vote in line with the Trump position just 19 percent of the time. That’s a bigger pro-Trump gap than any other Democrat in the Senate.

How often Democratic senators vote with Trump Difference between a member’s actual and predicted Trump-support scores MEMBER STATE TRUMP SCORE PREDICTED SCORE TRUMP PLUS-MINUS Dianne Feinstein CA 31.3% 19.2% +12.1 Mazie K. Hirono HI 26.5 17.9 +8.6 Brian Schatz HI 26.5 17.9 +8.6 Benjamin L. Cardin MD 26.5 20.7 +5.8 Patrick J. Leahy VT 24.5 20.7 +3.8 Mark R. Warner VA 42.9 43.0 -0.1 Chris Van Hollen MD 20.8 21.1 -0.3 Charles E. Schumer NY 22.4 23.1 -0.6 Maria Cantwell WA 26.5 28.7 -2.2 Kamala D. Harris CA 16.3 18.8 -2.5 Tammy Duckworth IL 24.5 27.2 -2.7 Thomas R. Carper DE 30.6 33.3 -2.7 Angus S. King Jr. ME 44.9 47.6 -2.7 Christopher Murphy CT 27.1 30.5 -3.4 Robert Menendez NJ 25.0 28.8 -3.8 Christopher A. Coons DE 29.2 33.8 -4.6 Richard J. Durbin IL 21.3 26.2 -4.9 Edward J. Markey MA 14.6 20.7 -6.1 Jack Reed RI 22.4 28.7 -6.2 Sheldon Whitehouse RI 22.4 28.7 -6.2 Patty Murray WA 22.4 28.7 -6.3 Bernard Sanders VT 14.3 20.7 -6.4 Elizabeth Warren MA 10.2 20.3 -10.1 Tim Kaine VA 32.7 43.0 -10.3 Richard Blumenthal CT 18.8 30.5 -11.7 Michael F. Bennet CO 30.6 43.8 -13.1 Catherine Cortez Masto NV 34.7 48.7 -14.0 Kirsten E. Gillibrand NY 8.2 23.1 -14.9 Martin Heinrich NM 22.4 38.0 -15.5 Cory A. Booker NJ 14.3 30.1 -15.8 Ron Wyden OR 16.3 33.9 -17.6 Tom Udall NM 20.4 38.0 -17.6 Bill Nelson FL 36.7 56.3 -19.6 Amy Klobuchar MN 30.6 50.5 -19.9 Jeff Merkley OR 12.2 33.9 -21.7 Margaret Wood Hassan NH 30.6 53.0 -22.4 Jeanne Shaheen NH 30.6 53.0 -22.4 Al Franken MN 25.0 49.6 -24.6 Gary C. Peters MI 29.2 54.2 -25.0 Debbie Stabenow MI 28.6 54.2 -25.7 Robert P. Casey Jr. PA 28.6 55.3 -26.7 Tammy Baldwin WI 20.4 55.4 -35.0 Joe Donnelly IN 47.9 84.8 -36.9 Joe Manchin III WV 55.1 93.6 -38.5 Sherrod Brown OH 30.6 70.3 -39.6 Claire McCaskill MO 43.8 84.6 -40.8 Heidi Heitkamp ND 51.0 92.9 -41.9 Jon Tester MT 38.8 86.1 -47.3

California just passed legislation to become a “sanctuary state,” a move that has been met with displeasure by the Trump administration. De Leon seems likely to play up the state’s need to assert itself as a powerful bloc of resistance to Trump.

In recent weeks, local news sources have noted de Leon’s rebukes of Feinstein, whom he paints as sympathetic to Trump. In August, after Feinstein said Trump “can be a good president” if he were to “learn and change,” de Leon hit back, saying, “It is the responsibility of Congress to hold him accountable — especially Democrats, not be complicit in his reckless behavior.” Most recently, de Leon pushed back against Feinstein’s comments that the recent massacre in Las Vegas couldn’t have been prevented by changes in gun laws because the shooter had passed background checks.

National Democrats like House Minority Leader Nancy Pelosi and fellow California Sen. Kamala Harris have voiced their supported for Feinstein, but she reportedly pushed up the announcement that she would run for re-election to this week out of worry that de Leon would announce soon. After Feinstein’s re-election announcement, Rep. Ro Khanna said that Feinstein was “out of touch” and that it was time for Democrats to “move on” from the 84-year-old senator. Asked about possible alternatives, Khanna floated not de Leon, but Rep. Barbara Lee or former Labor Secretary Robert Reich.

Whoever jumps into the race, Feinstein’s 2018 looks like anything but smooth sailing.