DOVER, Del. — A battle between Delaware's senior senator and an upstart challenger riding an antiestablishment wave within the Democratic Party highlights the state's primary elections Thursday.

Sen. Tom Carper, 71, has never lost a race in more than four decades in politics.

Carper's primary challenger is political newcomer and community activist Kerri Evelyn Harris, 38.

Carper, who famously says he always campaigns as if he's 20 points behind, is taking no chances against Harris, an Air Force veteran trying to stage one of the most shocking upsets in modern Delaware political history.

Carper has enjoyed a huge fundraising advantage against Harris this year, having raised more than $1.3 million as of mid-August, compared to a little more than $120,000 by Harris. He has far outspent her as well.

Despite being a frequent and vocal critic of President Donald Trump, Carper has developed a reputation over the years as a centrist able to work with both Republicans and Democrats in Congress.

"Delaware's always gotten rewarded for working to the middle, finding consensus. ... I don't think that's changed," he said.

That middle is largely occupied by people who aren't registered with either leading party, but independents have no voice in Delaware's closed primaries, in which only Democrats and Republicans can vote for their respective nominees. Polls were to remain open from 7 a.m. until 8 p.m.

Harris is among a wave of young activist Democrats, emboldened by the 2016 presidential campaign of U.S. Sen. Bernie Sanders of Vermont, trying to push the party farther left. Black, gay and female, her previous experience includes loading giant cargo planes, repairing cars and frying chicken in convenience stores, along with coaching young people to work for social change.

These candidates have sent shock waves through the party establishment, starting in June with a New York congressional primary victory by 28-year-old newcomer Alexandria Ocasio-Cortez over a 10-term incumbent. Recent victories by Tallahassee Mayor Andrew Gillum in Florida's Democratic gubernatorial primary and Boston City Councilor Ayanna Pressley in a closely watched congressional primary in Massachusetts have further energized the movement.

"People of the entire United States realize that this campaign has implications that can be resounding for the rest of the nation," Harris said, noting that more than 40 states are represented in the donations and assistance her campaign has received. "It's an effort to move the Democratic party closer to the people."

Delaware Republicans, meanwhile, are holding their own Senate primary, pitting former PayPal executive Gene Truono against Sussex County Councilman Rob Arlett. Republican voters also will decide between actor and retired railroad industry worker Lee Murphy and businessman Scott Walker as their nominee for Delaware's lone U.S. House seat, currently held by first-term Democrat Lisa Blunt Rochester.

Other statewide primaries to be decided Thursday include a four-way Democratic primary for attorney general and a three-way Democratic primary for state auditor. Seventeen legislative primaries also will be decided on the local level.