Whether the center of California’s political scale has shifted dramatically will be measured by what happens if Senator Dianne Feinstein faces a challenge if she stands for re-election.

Noted as a political centrist during her career as San Francisco supervisor, mayor and United States Senator, the political dynamics of California have altered over the 40-year span Feinstein held office. Whether the center holds would be tested if a well-known Democrat challenges Feinstein from the left and whether the Republicans mount a credible candidate for her job in 2018.

It would also be an opportunity for the growing segment of independent or the no-party-preference voters to flex their political muscle.

Recently, Sen. Feinstein made pronouncements that irritated the vociferous left wing of the California Democratic Party. Her suggestion to be patient with President Trump and waving a warning flag that DACA, as an executive order, was on shaky legal ground, raised howls of backlash from liberals.

As top Democratic political consultant Garry South told the Sacramento Bee, “The Democratic electorate has gotten more liberal, it’s gotten younger and it’s gotten far more diverse.” And: “The ground has shifted underneath everyone’s feet, almost like a sudden earthquake, and whether she understands that or not I don’t know.”

A challenge for Feinstein could come from ambitious, young Democrats looking to move up. Senate President Pro Tem Kevin de León, who will be termed out of office, is often mentioned as a possible challenger, especially after he rebuked Feinstein over her comments offering Trump “patience.”

No Republican of stature has indicated a run for the office. If no well-known Republican runs and Feinstein is challenged by a credible candidate on the left, an interesting dynamic comes into play.

This would not be a repeat of the 2016 senate race between Kamala Harris and Loretta Sanchez. In that race, those opposed to Harris and her left-leaning politics tried to pump up Sanchez as a centrist candidate but there were few takers.

Feinstein, unlike Sanchez, is well known and has plenty of money in both her campaign kitty and her personal bank account.

Mark Baldassare, president of the Public Policy Institute of California, and chief of the frequent PPIC polling efforts, says independent voters could make a difference in an all-Democratic senate race. “Most independent voters are in the middle of the road,” Baldassare said. He added that these voters make decisions on candidates based on policy matters.

Voters not associated with any political party now make up one-quarter of the state’s registered voters and are only 1.5 percentage points behind Republican registration. A race between a centrist like Feinstein and a more liberal candidate could give these independents a cause and a reason to vote.

Feinstein’s success or failure against a challenge from the left will tell us how far the center has moved on California’s political scale.