Sen. Dianne Feinstein Dianne Emiel FeinsteinMcConnell says Trump nominee to replace Ginsburg will get Senate vote Top Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence Intensifying natural disasters do little to move needle on climate efforts MORE (D-Calif.) holds a commanding lead over her progressive primary challenger, state Senate President pro tempore Kevin de León (D), according to a new poll from the Public Policy Institute of California.

The poll found that Feinstein currently leads de León 46 percent to 17 percent among likely voters in the state, while 33 percent of likely voters said they were undecided.

The poll illustrated de León's uphill battle to unseat Feinstein, who is seeking her fifth term in Congress's upper chamber.

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De León, who has presided over a Democratic supermajority in the state Senate, is largely unknown on a national level.

He has launched a series of attacks on Feinstein from the left, slamming her for voting in favor of 11 of President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE's Cabinet nominees and for her support for stronger immigration restrictions.

However, Feinstein has become a major voice on immigration in recent months.

She notably asked Trump in a televised meeting last month to support a “clean” bill to reauthorize the Deferred Action for Childhood Arrivals program.

Immigration is considered to be a hot-button issue in California.

The Public Policy Institute of California poll was conducted from Jan. 21 to 30 among 1,705 adult residents in California.

The study's margin of error is 3.2 percentage points for all adult voters and 4.35 percentage points for the 1,042 likely voters.