This story has been updated to include independent and third-party candidates and a more complete fundraising figure for Sen. Cardin.

Two-term Sen. Benjamin L. Cardin (Md.) is considered the overwhelming favorite to secure the Democratic nomination on Tuesday and be reelected in the fall.

Cardin, 74, has represented the state in Congress for over 30 years and is the former ranking Democrat of the Senate Foreign Relations Committee. He maintains broad popularity among Marylanders — winning 61 percent support among Democratic voters in a recent Goucher poll — and raised over $4 million in the most recent election cycle.

“At no point has there been any indication that voters weren’t satisfied with the job he was doing,” said Todd Eberly, a political-science professor at St. Mary’s College of Maryland.

Still, a total of 21 other candidates — including 11 Republicans and seven Democrats — are seeking their party’s nomination for the seat this year for reasons that range from his “no” vote on the Iran deal to greater representation for women and disabled people in Congress.

Cardin’s primary opponents include Chelsea Manning, the government whistleblower and former intelligence analyst, and Jerome “Jerry” Segal, a philosopher and progressive activist.

Manning, who was convicted in 2013 for the largest leak of classified documents in U.S. history, made waves when she announced her candidacy in January. But her insurgent campaign has faltered since, with scant appearances and fundraising.

Chelsea Manning (Markus Schreiber/AP)

“The establishment needs to be challenged, and it needs to be challenged in their footholds and in the places where they feel safe,” she told The Post in an interview earlier this year, vowing not to accept a single corporate dollar.

In May, Manning — who moved to Rockville after President Barack Obama commuted her prison sentence — posted to Twitter a photo of a person on the ledge of a building. The photo was later deleted, with her account saying that she is “safe.”

At the time, Kelly Wright, Manning’s communications director, said that the campaign had not been suspended. Wright did not respond to repeated requests for comment this week.

Segal, 74, a longtime critic of Israel’s occupation of the Palestinian territories, said he is looking to attract voters who oppose Cardin’s strong support for Israel and close ties to the American Israel Political Affairs Committee. A decent showing in his favor, Segal said, would demonstrate that politicians like Cardin could face electoral consequences for aligning themselves with the powerful lobby group.

Jerome “Jerry” Segal (Segal campaign)

“If I can make that point, then the whole mystique of AIPAC’s influence will fall,” said Segal, who condemned the opening of a U.S. Embassy in Jerusalem as well as Cardin’s “no” vote on the Iran nuclear deal. “If I knock out the big dog, the whole sleigh comes to a halt.”

A philosophy and finance double-major in college, Segal sold his stocks in Apple to finance over $250,000 in newspaper ads that call himself “Maryland’s Bernie Sanders.”

In addition to expounding on Segal’s socialist platform for greater opportunity and equality, the ads attack Cardin for refusing to debate his Democratic challengers.

Sue Walitsky, Cardin’s spokeswoman, said in a statement that the senator has attended or “made every effort to send a surrogate” to candidate forums organized by third-party groups.

Other Democrats in the race:

●Marcia Morgan, a retired flight attendant from Montgomery County, who said she is running in the Democratic primary because “Maryland needs to be represented by a woman.”

●Restaurant owner Rikki Vaughn, 37, who said Cardin “takes voters for granted.”

Debbie “Rica” Wilson (Wilson campaign)

●Debbie “Rica” Wilson, 43, a nonprofit director in Charles County. As a disabled African American woman, she said she is running to increase representation for marginalized groups in Congress.

Lih Young, of Montgomery County, declined to answer a reporter’s questions, and Erik Jetmir, a Navy Reserve officer in Prince George’s County, did not respond to a request for comment.

In the crowded Republican primary, just two candidates — lawyer Christina Grigorian and political scientist Tony Campbell — have raised or spent enough money to register with the Federal Election Commission.

Grigorian, a 49-year-old partner at the D.C. law firm Katten Muchin Rosenman, is campaigning as a moderate who can promote economic growth and appeal to families and business owners.

A practicing Catholic who is pro-choice, she is also the only woman in the Republican primary — a perspective that she said helps broaden her appeal.

Grigorian was born and raised in Baltimore County and got her law degree at the University of Maryland. She and her family live in Bethesda. “You don’t get much more of a Maryland story than mine,” she said.

Antonio “Tony” Campbell. (Campbell 4 Maryland)

Christina Grigorian. (Thomas Hedges)

Campbell, a political-science lecturer at Towson University in Baltimore who was state chairman for Ben Carson’s 2016 presidential campaign, is more conservative, backing local control of education policy and school choice.

He was appointed by Gov. Larry Hogan (R) to the state’s P-20 Leadership Council, which works on preparing students for the workforce, and also serves on education oversight committees in Baltimore County.

Campbell said he would work on reforming health care for veterans — an issue he dealt with personally while working as an Army chaplain, when soldiers approached him with thoughts of suicide. He has been endorsed by one of the state’s prominent African American conservatives: former lieutenant governor Michael Steele.

Evan Cronhardt (Aaron Chiusano)

Nnabu Eze (Nnabu Eze campaign)

Other Republican candidates:

●Evan Cronhardt, 32, of Anne Arundel County, who said he wanted to address his frustrations navigating Medicare and Medicaid after becoming disabled.

●Nnabu Eze, 48, an IT contractor in Pikes­ville who immigrated from Nigeria and said he wants to “fight the corrupt system in American politics.”

●Bill Krehnbrink, 71, a retired teacher and Vietnam War veteran from Baltimore County who is running on the slogan “Egg,” short for “Everybody’s Gotta Go.”

Gerald Smith (Smith campaign)

●Gerald I. Smith Jr., 46, a Temple University master’s student who lives in Cecil County and said he wants to support Hogan’s agenda from the Senate.

● Blaine Taylor, 71, a retired author and Vietnam War veteran in Towson, who said he wants to “prevent Civil War at home.”

Blaine Taylor (John Durand)

Republicans Chris Chaffee of Calvert County and Albert Binyahmin Howard and John R. Graziani, both of Anne Arundel County, did not respond to requests for comment.

The 11th Republican, Brian Charles Vaeth, said he is no longer seeking the seat, although his name remains on the ballot.

Neal Simon, a financial services executive from Potomac, is running as an independent and will face the winners of the Democratic and Republican primaries in November. Steve Gladstone, a computer programmer in Baltimore County, also is running as an independent.

Mia Mason, a transgender Navy veteran and reservist in Frederick County, is seeking the Green Party nomination, and Arvin Vohra of Montgomery County, the vice chair of the Libertarian National Committee, is seeking that party’s nomination.