Democrats Kamala Harris and Loretta Sanchez have scarcely criticized one another during their year-long campaign for the open Senate seat in California.

But that would change if, as polls during the past week have predicted, both women emerge as the winners of Tuesday’s primary, the first leg in the race to replace retiring Democrat Barbara Boxer.

A general-election face-off between Harris, California’s attorney general, and Sanchez, who has been a House member for two decades, could become one of the season’s most contentious races, testing party loyalties and political alliances between racial and ethnic groups.

Under the state’s primary system, the top two vote-getters, regardless of party, advance to the general election. Harris has consistently led in public polling since declaring her candidacy 18 months ago. Sanchez has polled a distant, but solid second. A survey released on Friday by the Field Poll showed Harris with 30 percent support among likely voters, followed by Sanchez with 14 percent. An NBC News-Wall Street Journal-Marist poll that came out Thursday put Harris’s support at 37 percent, with 19 percent for Sanchez.

The Field Poll shows Sanchez leading Harris among Latinos 32 to 21 percent and among voters under 30 by 29 to 20 percent. Harris leads in all other categories, including age, geography and other racial and ethnic groups.

Polls also have consistently shown that a large number of voters — between 24 and 30 percent — remain undecided in a race that features Harris, who would be the chamber’s only African-American woman and has some national buzz, and Sanchez, who has the chance to make history as one of the first Latinas elected to the Senate.

“Poll after poll shows Kamala Harris with a commanding lead ahead of the June 7 primary, and our campaign is working hard to finish in the strongest possible position on Tuesday, ” said Harris campaign spokesman Nathan Click.

The idea of two Democrats emerging from the Senate primary on Tuesday is made more likely by the tight Democratic presidential primary also on the ballot in California. Hillary Clinton and Bernie Sanders are locked in a close race, while Donald Trump has already secured the GOP presidential nod. That means Democratic turnout is likely to be higher up-and-down the ballot while Republicans might not feel the need to vote.

In all 34 candidates are competing for the first open Senate seat in California in 24 years. The Golden State is deep blue, so the contest would be more competitive if two Democrats emerge from the open primary rather than a Democrat and Republican.The state’s heavy Democratic lean is evident in the Senate race polling: not one of the dozen Republicans running in the primary has polled higher than 10 percent in recent months and surveys during the past week showed them running in the low single digits.

“This is symptomatic of California becoming a one-party state,” said Mike Madrid, a Republican consultant. “There aren’t enough well known Republican politicians that have strong name ID nor the ability to raise the money required to build it in a state this size – as a result a huge swath of voters have no idea who is running or what they stand for.”

Harris, 51, grew up in the San Francisco Bay Area — her mother, who is from India and her Jamaican-born father met as graduate students. She is the first woman, African-American and Asian-American to be elected attorney general. Some groups representing black women, one of the Democratic Party’s most loyal constituencies, have rallied national support for Harris’s candidacy because there hasn’t been a black woman in the Senate since Carol Moseley-Braun (D-Ill.) left in 1999.

Sanchez, 56, whose congressional district is in Orange County in southern California, is the daughter of Mexican immigrants who proudly tells audiences that her working-class family “sent two daughters to the U.S. Congress.” Her sister, Linda Sanchez, represents suburban Los Angeles County. National Hispanic political organizations are backing her campaign, seeing it as chance to finally elect a Latina to the Senate.

Luis Vizcaino, spokesman for the Sanchez campaign, said the congresswoman started out a year ago at 8 percent in the polls, but has “run a very effective” campaign and now appears to have a lock on second place. “Once we advance to the general, the electorate changes in her favor,” Vizcaino said, noting that more Southern Californians and Latinos vote in general elections.

Harris has some important allies, however.

California Gov. Jerry Brown (D) is backing her, as well as the state Democratic Party, which chose Harris 78 percent to 19 percent, after both candidates campaigned for the support of  rank-and-file party leaders. The move drew a rebuke from Texas Rep. Filemon Vela (D), who said the party’s action was “insulting to Latinos all across this country” because it was not giving Sanchez a level playing field on which to compete for the seat.

For much of the past year of campaigning, Harris and Sanchez have not not engaged each other.

The barbs have instead come from their Republican competitors. They have accused Harris of not aggressively pursing Democratic officials accused of public corruption, but investigating anti-abortion rights groups while accepting the support of abortion rights groups. Harris has dismissed the criticisms, arguing “we will go where the facts lead us.” She has further frustrated her opponents and journalists by declining to discuss the cases, noting that the state of California and its agencies also are her clients.

Republicans have chided Sanchez, who touts her membership on the House Armed Services and Homeland Security, for missing committee meetings. Sanchez said that the committees often meet at the same time and she can’t be in two places at once.

Sanchez has also brought unwanted scrutiny on herself, including a statement last year in which she claimed “between 5 to 20 percent” of Muslims “have a desire for a caliphate and to institute that in any way possible.” Sanchez rejected criticism that her comment was an attack on U.S. Muslims and has argued that statistic has been widely used by other commentators.

The three Republicans who have gotten the most support in polls have been unable to chip into the Democrats’ leads. Two of them said over the weekend they believe they will pull off upsets on Tuesday, but both are aiming for second, not first place.

Duf Sundheim, 63, a former state party chairman, cited an online poll that showed him just 5 points behind Sanchez among voters who have already cast absentee ballots. “I think we have a realistic shot,” Sundheim said. “Do I think we’re gonna run away with second place, no.”

Tom Del Becarro, 54, also a former GOP state chairman, says he’s best positioned to overtake Sanchez on primary day. Del Becarro said he has the support of anti-tax, anti-abortion and gun rights activists, groups that can help mobilize voters. “I like my alliances versus the other people vying for No. 2,” Del Becarro said. “We will do better than people think.”

Another GOP candidate, Ron Unz, 54, a Silicon Valley entrepreneur best known for championing a law effectively eliminating bilingual education in public schools, is not as optimistic about his prospects on Tuesday. He referred to the The Field Poll showing five GOP candidates each with 3 or 4 percent support — “all far below Sanchez.”

“I’m afraid that I’m pretty sure that the polls are quite accurate, with Harris and Sanchez almost certain to take the top two spots,” he said in an email.