A veteran congressional aide has jumped into the race to succeed retiring U.S. Rep. Frank R. Wolf in Northern Virginia, expanding a Republican field that could grow even more in the coming days.

Robert Wasinger, a Kansas native who has lived in Virginia for nearly two decades, is leaving his post as chief of staff to Michigan Rep. Kerry Bentivolio (R) to enter the contest for the 10th district, which stretches from McLean to the West Virginia border and is considered battleground territory by both parties.

Wasinger joins Del. Barbara J. Comstock (Fairfax); Richard C. Shickle, chairman of the Frederick County Board of Supervisors; Stephen Hollingshead, an official in the administration of President George W. Bush; and Marc Savitt, head of the National Association of Independent Housing Professionals, in the GOP nomination fight. Wasinger made clear in an interview that he planned to run at his foes from the right.

“I fear that conservatives are not going to be well-represented with the choices that are out there now,” Wasinger said. “I’m going to run an insurgent, aggressive grass-roots campaign.”

Since state Sen. Richard H. Black (R-Loudoun) dropped out of the race last month, momentum has appeared to build behind Comstock. She has deep ties to state and national GOP leaders, and last week picked up the endorsement of the chairman of the Republican Party of Virginia, Pat Mullins.

But at least two other Republican candidates are still eyeing the race: Del. Robert G. Marshall (Prince William) and former Pentagon official Howie Lind.

Marshall — an outspoken conservative, particularly on social issues — made unsuccessful bids for U.S. Senate in 2008 and 2012. Several Republicans said he was considering a run for Wolf’s seat, but he was coy this week when asked about his plans.

“I learned to play poker when I was 5 years old. That’s my answer,” Marshall said.

Lind, meanwhile, recently quit the U.S. Senate race against Sen. Mark Warner (D) after concluding he could not beat former Republican National Committee chair Ed Gillespie for the GOP nomination. Now he’s also mulling a campaign in Wolf’s 10th district.

“I am considering it, but I have not made a final decision,” Lind said in an e-mail Monday.

Wasinger, 42, lives in Fairfax Station and has 11 children. He is no stranger to the campaign trail. In 2010, he ran for an open congressional seat in his native Kansas and came in a distant fourth, though he did manage to raise more than $800,000 for his effort.

Wasinger was also the manager of Sam Brownback’s 2008 presidential campaign and served as chief of staff in Brownback’s Senate office.

Republicans will choose their nominee in an April 26 “firehouse primary,” which has fewer polling places than a regular primary and is run by the party rather than the state.

On the Democratic side of the 10th district race, Fairfax County Board of Supervisors member John W. Foust is considered the front-runner, ahead of Fairfax lawyer Richard Bolger, Leesburg architect Sam Kubba and Marine Corps veteran David R. Wroblewski.

Karen Schultz, a Shenandoah University professor, is also considering a run for the Democratic nod.

Michael Laris contributed to this report.