Richard Mattox, left, and Ronald Hobson, center, greet Virginia Rep. Robert C. "Bobby" Scott before he hosts a roundtable in Alexandria. (Linda Davidson/The Washington Post)

In a tradition he has kept for 40 years, Rep. Robert C. “Bobby” Scott threw open his family’s sprawling back yard for a Labor Day cookout, a ritual that marks the real start of the political season in this state.

But this year, an undercurrent of intrigue pulsed through the gathering: As he welcomed several hundred guests, Scott (D-Va.) was also launching his unofficial bid for a U.S. Senate seat that is not yet open.

“This is a big year for our potential United States senator, Bobby Scott!” Scott’s niece, state Del. Marcia “Cia” Price (D-Newport News), shouted to the crowd. “The nation is watching Virginia. . . . We have to show that we have his back.”

As the senior Democrat in Virginia’s congressional delegation, Scott, 69, has emerged as the front-runner to fill Tim Kaine’s Senate seat if Democrats win the White House in November and Kaine becomes vice president.

The first African American to serve in Congress from Virginia since the 1890s, Scott would again break the color barrier if Gov. Terry McAuliffe (D) appoints him as the first black senator from the commonwealth.

Virginia Rep. Robert C. "Bobby" Scott in Alexandria. (Linda Davidson/The Washington Post)

Yet for all the symbolism and feel-good value of such an appointment, some Democrats privately express reservations about entrusting a seat that could decide the balance of power in the closely divided Senate to a candidate who has never won statewide, is considered less than dynamic and has been an anemic fundraiser.

The concerns are magnified by the singular challenge faced by anyone appointed to fill Kaine’s seat: That candidate would assume office in January 2017, run in a special election in November, and then turn around and run again for a full term the very next year.

The only person to pull off that political hat trick in the nation’s modern history was, coincidentally, another Virginian: Harry F. Byrd Sr., the patriarch of the conservative Democratic machine that blocked the desegregation of Virginia’s public schools.

Ironically, Byrd’s strategy of “massive resistance” to the Supreme Court ruling in Brown v. Board of Education prompted Scott’s father to send his son to an elite private boarding school in Massachusetts at age 12.

If Kaine becomes vice president, Virginia would probably host the only Senate race in the country in 2017, and, depending on the outcome of this year’s election, control of that chamber could hinge on the Virginia seat. The high stakes would attract donors — and pressure: Hillary Clinton, if elected, would need a Senate majority to confirm Supreme Court justices and other appointments and to further her agenda.

“We’re talking about a Senate that could be on a knife’s edge,” said David Wasserman, House editor for the Cook Political Report. “It could truly take on a national import.”

McAuliffe has said about 20 people have indicated an interest in the seat, but he refuses to discuss potential appointees, aside from saying he wants a diverse congressional delegation.

Those close to him say that, in addition to Scott, he would have to consider Rep. Don Beyer (D-Va.), a former lieutenant governor and ambassador in the Obama administration who can raise the cash to run statewide. Another possibility is Del. Jennifer L. McClellan (D-Richmond), a corporate attorney who led McAuliffe’s transition team and considers Kaine her political mentor. She would be the second-ever African American woman in the Senate.

Political observers in Virginia and around the country say Scott deserves the right of first refusal — and not only because his appointment would make history and cement McAuliffe’s legacy as a champion of minorities.

Although Scott lacks a signature policy achievement, elected officials from both parties say he has forged a reputation as a hard worker and policy wonk over a 40-year public career, first in the General Assembly and then in Congress. His work has focused on civil rights and criminal-justice reform, timely issues as the nation debates sentencing as well as the relationships between police and communities. He is the ranking Democrat on the House Education and the Workforce Committee.

Scott was one of three members who voted against the rosy-sounding Justice for Victims of Trafficking Act of 2015 because it created a new mandatory minimum prison sentences.

“There are a great many folks in Congress whose knowledge on these issues is about as thin as the piece of paper it’s written on,” said Cornell William Brooks, president of the NAACP. “We’re at a moment in the nation’s history when we need people of substance.”

People like Scott, he said.

Pressure is building on McAuliffe, who was greeted with chants of “Bobby!” at a labor conference in Williamsburg last month, according to Virginia AFL-CIO President Doris Crouse-Mays.

A few weeks earlier, Scott was speaking to the Virginia delegation at the Democratic National Convention when McAuliffe walked in the room. Scott beamed and asked the crowd to welcome the governor — “my new best friend.”

Days after Clinton tapped Kaine as her running mate, the push for Bobby Scott began: The Congressional Black Caucus, former governor L. Douglas Wilder — himself the nation’s first black governor since Reconstruction — Virginia’s congressional delegation, and Lt. Gov. Ralph Northam (D), who is running for governor, all lined up behind him.

“He would be a great senator. Not good, great. One of the brightest members of the entire Congress,” Rep. Elijah E. Cummings (D-Md.) said in a phone interview.

Some Democrats, however, question the wisdom of committing to Scott, who has never faced a competitive reelection race in 24 years in Congress or raised more than $525,000. That’s a small fraction of the minimum $20 million experts say it costs to run statewide.

His biggest donors include the American Association for Justice, which represents trial lawyers; the National Education Association; public-sector unions; and — like most elected officials in Virginia — the Richmond-based utility giant Dominion Resources.

Scott’s persona is that of a policy wonk, someone more interested in details than dazzle. Even as he hosted his Labor Day cookout, he stood with his arms crossed and smiled sheepishly, leaving it to his niece to engage the crowd. Despite his decades in public service, Bobby Scott is not a household name in Virginia.

“He’s not demonstrated, until recently, an ambition for higher office,” said Quentin Kidd, a political scientist at Christopher Newport University in Scott’s district. “There’s an uncertainty whether he can raise money.”

Scott bristles at the suggestion he won’t be ready. “I’ve fundraised all I’ve needed to do to get 70 percent of the vote,” he said, cutting off a reporter who asked about finances.

His district was at the center of a federal redistricting lawsuit in which Democrats successfully argued that Republicans illegally concentrated black voters in his district. In other words, it was safely his from Day 1.

But Scott grinned behind his designer eyeglasses and invoked the famous story John F. Kennedy told about his father who wired, “Dear Jack, Don’t buy a single vote more than is necessary. I’ll be damned if I’m going to pay for a landslide.”

Scott added: “I’ll be able to raise what’s necessary.”

Rep. Gregory W. Meeks (D-N.Y.), chairman of the Congressional Black Caucus PAC, said members will help him raise cash and donors from around the country who want to see more African Americans in the Senate will send checks. Currently, there are two: Cory Booker (D-N.J.) and Tim Scott (R-S.C.)

“Just because he hasn’t had to do it doesn’t mean he can’t do it,” Meeks said.

Bobby Scott said he plans to ramp up fundraising and hire staff in anticipation of the fight ahead.

His presence on the ballot in 2017 — with statewide elections for governor, lieutenant governor and attorney general — could help Virginia Democrats turn out their voters. President Obama won the state twice, but Democrats have had a harder time winning in off-year elections, when turnout typically drops off dramatically.

“There’s no one more experienced than Bobby Scott at earning African American votes,” Wasserman said.

To that end, Scott has worked hard for Clinton, attending at least a dozen office openings and rallies since February, including seven after Kaine joined the ticket.

Hours before boarding a flight to a recent education conference in Detroit, Scott campaigned for Clinton among black busi­ness­ leaders at the Northern Virginia Urban League. Scott joked that, among African Americans, Trump ranks fourth in a two-way race.

“I’ve always been insulted with the term ‘African American outreach,’ ” he told the group, adding that the phrase suggests a campaign has to go outside itself to find black voters.

Then someone asked how Clinton could inspire young people the way Sen. Bernie Sanders (Vt.) had. Scott responded with logic.

“You got a choice,” he said. “Either Clinton or Trump will be president. The stark contrast makes it hard for me to imagine what the confusion is.”

More professor than politician, Scott struggles to deliver a sound bite. A simple question elicits a methodical treatise, full of facts and historical data, about why the other side must be wrong — which it often is, according to Scott.

He arrived in Congress in 1993, after working on criminal-justice reform in the state legislature, and promptly voted against President Bill Clinton’s crime bill.

“If you look back and check the transcripts,” Scott said, “I could have written those things last week. . . . You really have a choice with crime policy: You can reduce crime and save money; or you can codify slogans and sound bites and do nothing about crime and load up the prisons. We now lock up a higher percentage of our population than any country on earth. By far.”

Scott says he has fought to push through incremental policy initiatives that matter to his Hampton Roads constituency.

He helped shape the Fair Sentencing Act of 2010, which reduced the sentencing disparity between crack and powder cocaine. And he sponsored the 2014 reauthorization of the Death in Custody Reporting Act, requiring state and local police to tell the federal government when someone dies in custody or during an arrest.

The Justice Department has lagged in enforcing the law, frustrating Scott.

His aides say it’s too early to discuss strategies for a Senate run but noted that Scott won competitive state Senate races in a predominantly white district.

True to his low-key style, Scott is relying on others to carry his message to McAuliffe, which may or may not be the best strategy.

At his cookout, the band leader called Democratic bigwigs to the stage, singing “It’s Our Time.” Northam; Kaine’s wife, Anne Holton; and dozens of local elected officials, including mayors and city council members, gathered around Scott in front of the stage under an enormous honey locust tree.

Only McAuliffe stayed home.