Sen. Ben Cardin, D-Md., speaks on the financial reform bill on Capitol Hill in Washington, D.C. in 2010. (Charles Dharapak/AP)

Sen. Benjamin L. Cardin’s reelection race has become more like a stroll, with a new Washington Post poll showing most Marylanders ready to give him a second term next month.

And with the last-minute entry into the race of an independent upstart with money to burn on television ads, Cardin’s seat appears even safer. The most closely followed element of Maryland’s Senate race seems to be whether the candidate without a party affiliation will edge out the GOP’s nominee for second place — and what that says about Maryland’s growing number of third-party and unaffiliated voters.

The wild card is Rob Sobhani, a former Georgetown University lecturer and international businessman. Polls suggest that he likely will take a sizable split of the anti-Cardin vote from former Secret Service agent Dan Bongino, the Republican Party’s nominee.

“You can compare him to Ross Perot — another wealthy businessman running in a time of economic trouble and criticizing the major parties,” said David Karol, associate professor of government at the University of Maryland.

In the new Post poll, Cardin (D) wins 53 percent among likely voters. Bongino wins 22 percent, while Sobhani — who entered the race in September — has 14 percent. (Libertarian Party candidate Dean Ahmad receives about 2 percent.)

Sobhani, who is running an almost entirely self-financed campaign, has spent more than $4.6 million, more than half of which has been put to work in ads. Suddenly, people on the street recognize him and his slogan.

“I really liked the ‘Declare your independence,’ ” said a woman who stopped him on the sidewalk during a campaign visit to downtown Frederick this month.

“I see him on the TV all the time,” said William Sears, 38, a graphic designer who watched the encounter from a few feet away. “He seems like a pretty well-grounded guy.”

Sears said that, as a Democrat, he would probably go for Cardin. But Sears said he would give some thought to voting for a nontraditional candidate like Sobhani, something a small but growing minority of Marylanders are doing.

Although Maryland is one of the bluest states, with Democrats outnumbering Republicans by more than 2 to 1, third-party and unaffiliated voters have been increasing. In 2000, they were a little more than 13 percent of registered voters, Maryland State Board of Elections data show. By 2004, the number was at 15 percent. Today they account for about 18 percent.

Matthew Crenson, professor emeritus in Johns Hopkins University’s Department of Political Science, said Sobhani’s relatively strong showing in the polls reflects disenchantment with the two major parties, especially the GOP.

Sobhani, 52, who was born in Kansas to Iranian immigrants, has shown a knack for making the most of his last-minute arrival on the scene. In 1990, when he was 30, Sobhani helped broker a huge international petroleum deal, as if by accident, between Amoco and Azerbaijan.

While teaching in Azerbaijan, Sobhani was invited for a private meeting with its newly installed president as the small Caucasus country was on the verge of inking a deal with British Petroleum for drilling rights to its abundant oil fields. Sobhani, who spoke Azeri, told the Azerbaijanis to think twice about the BP deal. Instead, as related by journalist Steve LeVine in his book, “The Oil and The Glory,” Sobhani urged Azerbaijan to consider a U.S. company with the full backing of a superpower.

“The American flag follows the American dollar,” he told them. Amoco rewarded Sobhani by putting him on its payroll.

After obtaining a doctorate at Georgetown, he settled in the Washington area and worked for former representative Connie Morella (R). He is the owner of Caspian Group Holdings, a company that specializes in energy and development, and lives in Potomac with his wife, Guilda, and two children.

Sobhani, who had run and lost as a Republican in the 1992 and 2000 primaries for U.S. Senate, petitioned his way onto the ballot as an independent. Although he’s vague on what he would do differently than his opponents, he often returns to the theme that he would use business as a centerpiece of foreign policy.

“I see opportunity in foreign policy for my state, which I don’t think Senator Cardin is even aware of,” Sobhani said

The novelty of Sobhani’s campaign appears to have come mostly at the expense of Bongino, another newcomer who boasts a colorful bio. Bongino, 37, grew up poor in New York — “We ate Cheerios for dinner,” he said in an interview — and became a New York City police officer. He picked up a psychology degree at City University of New York while with the NYPD and later an MBA at Penn State while working with the Secret Service. As a special agent, he served on President Obama’s security details. Then he resigned after 12 years to hit the campaign trail.

“We needed a legitimate outsider,” Bongino said.

His story was a hit with conservative media stars, getting him airtime with Sean Hannity, Glenn Beck and others. His wife, Paula, is a Web designer, and they have two daughters and live in Severna Park.

He has pledged to repeal the Obama health-care law, back school-choice programs such as vouchers and oppose new taxes.

“If you want someone to raise your taxes, I’m not your guy. You have two other choices,” Bongino said. On social issues, however, he shades closer to libertarian. He said he supports the decriminalization of marijuana and he thinks government should not be involved in sanctioning any type of marriage.

For Bongino, Sobhani’s campaign has been a multimillion-dollar sideshow to promote the businessman’s ego and perhaps future business prospects abroad. Bongino also disagrees that Sobhani’s support will come mostly from voters who lean Republican.

In the Post poll, Sobhani wins 19 percent among Republicans and independents who lean to the GOP. His base of support is clearly among political independents, where he wins 28 percent support, according to the poll.

Cardin, who turned 69 this month, has seemed to float above it all. He is well-known to Maryland voters, especially in the vote-rich Baltimore area, having been in politics since 1967. His campaign theme this year is simple: “My friend Ben.”

His opponents say Cardin has few pieces of legislation that he can point to as achievements. But Cardin’s supporters say he is more comfortable with wonkery than wheeling and dealing, and he has played an important role in safeguarding the Chesapeake Bay and pushing for Obama’s health-care overhaul. When members of Congress retreated after finding themselves under attack in town-hall meetings for their support of the Affordable Care Act, Cardin fought harder.

Earlier this month, at a forum sponsored by the Frederick County Commission for Women, Cardin gave a full-throated defense of his support for legislation supporting pay equity for women, health-care reform and a balanced approach to financial stability that included spending cuts and new taxes. He was unapologetic about his philosophy — that government exists primarily to lend a helping hand.

“We do need government as a partner,” Cardin said.

Jon Cohen and Peyton M. Craighill contributed to this report.