With just one branch and a small staff, Chain Bridge Bank has the unassuming feel of a local business. But the $230 million Beltway depository founded by ex-Sen. Peter Fitzgerald (R-Ill.) is fast becoming the preferred bank of the Republican Party.

The presidential campaigns for former Massachusetts Gov. Mitt Romney and Texas Gov. Rick Perry have accounts there, as do dozens of prominent political action committees run by Republican heavy hitters such as Sen. John McCain (Ariz.), Speaker John Boehner (Ohio) and former Alaska Gov. Sarah Palin.

Prominent conservative groups such as American Crossroads and the American Conservative Union, which hosts the annual Conservative Political Action Conference in Washington, D.C., have also banked there.

Though the bank is nonpartisan and has had among its clients the Democratic Blue Dog PAC, many of its founders and leaders move in Republican fundraising circles and draw political clients from them. It’s a business model that has worked: Chain Bridge’s earnings were up 48 percent last year from the year prior, according to Marketwire.

“Certainly all of us have worked hard to get the business of our friends and associates,” said Fitzgerald, who left Congress after a single term in 2005 and founded the bank two years later. He serves as chairman of Chain Bridge.

Fitzgerald and other employees of the bank, including Executive Vice President John Vogt, gave more than $208,000 to the campaigns of Republican candidates and to conservative organizations and PACs since 2008, according to the Center for Responsive Politics. Fitzgerald and Vogt have also publicly supported the Romney presidential campaign, which has an account at the bank.

Many of Chain Bridge’s advisory board members are also part of the political scene. Some are lobbyists, and others run trade associations. Expertise in those areas helps the bank understand customers’ needs, Vogt said.

“We know inherently what they are and how they operate,” he said. Vogt, a former lobbyist, added that he brought to the bank a “Rolodex of 30 years downtown.”

The bank’s business model could create a campaign finance minefield. Federal regulations prevent banks from offering to political accounts the kind of discount fees or low interest rates they may offer to lure big corporate accounts.

“If you’re giving a candidate a special deal … the result could be found to be making a prohibited contribution to the campaigns,” said Lawrence Noble, a campaign finance lawyer at Skadden, Arps.

Fitzgerald and Vogt said Chain Bridge is careful not to give anyone special treatment. They also point out that the bank has had rival candidates as customers at the same time. During the Virginia gubernatorial election of 2009, Chain Bridge managed the accounts of Republican Gov. Bob McDonnell and Democratic primary contender Terry McAuliffe.

Vogt also noted with pride that the Perry campaign chose Chain Bridge despite Vogt and Fitzgerald’s support for Romney.

“They wanted to bank here for their presidential campaign anyway, because they acknowledge that we are ready for prime time,” Vogt said.

Customers of the bank said they are drawn to it because Chain Bridge employees understand and accommodate their needs. The bank offers late wire transfers that come in handy during the thick of a political campaign and bank staff members print their cellphone numbers on business cards.

Instead of building branches all over town, Chain Bridge has focused on buying technology that lets its political clients scan checks to make remote deposits when on the road.

Rob Zimmer, founder of Votesane PAC, said Chain Bridge understood his needs when many others “scrunched up their faces” at his PAC’s structure. The citizen advocacy site lets users make donations to any candidate, regardless of party. The PAC spent $15,000 during the midterm elections.

“Chain Bridge said, ‘Yep, OK, we get it. We think we know what you need,'” Zimmer said, and then the bank delivered.

Chain Bridge Bank doesn’t offer legal advice, but Zimmer said it has also helped that the bank’s staff is versed in campaign finance law.

“They know the room for error is basically zero,” he said.

Emily Buchanan, executive director of the Susan B. Anthony List, said her conservative anti-abortion group chose Chain Bridge for similar reasons. With more than 60,000 low-dollar donors and thousands of small donations, Buchanan said, her group was willing to pay more for a bank that met its demands. The group spent $700,000 during the 2010 elections.

“They understand the speed at which we operate and the time-sensitive nature, especially during election periods,” Buchanan said.

Not all of Chain Bridge’s clients are overtly partisan. Trade associations and corporate PACs also bank with Chain Bridge, as does satirist Stephen Colbert’s super PAC. K Street customers include C2 Group, Daryl Owen Associates, Capitol Solutions Government Relations, Jochum Shore & Trossevin and Capitol Hill Strategies.

Fitzgerald insists he did not set out to build a political bank but a local one that serves the community of McLean, Va. Many of the banks clients are personal account holders and small businesses not tied to the political scene.

“The bank’s clientele is really representative of what the industry is in the Washington, D.C., area,” Fitzgerald said.

He attributes some of the bank’s success to its “very clean balance sheet” in 2007, when many of the larger banks were struggling with subprime mortgages.

“Not only did we not have any bad loans, we had very few loans,” Fitzgerald said. The bank also did not take any Troubled Asset Relief Program money, a selling point for some conservatives opposed to President Barack Obama’s financial recovery efforts.

As a Senator, Fitzgerald famously offered the sole opposition to an airline bailout after 9/11, asking on the Senate floor, “Who will bail out the American taxpayer?”

He continues to comment on current fiscal policy and has chided the deficit solutions offered by both parties. Fitzgerald also continues to help candidates raise money, political activism that helps boost his profile and the bank’s.

“Of course, we are a relationship-oriented bank, so personal relationships are very important,” he said.

Correction

The article misstated the job title for Emily Buchanan, executive director of the Susan B. Anthony List.