Donald Trump speaks during a Liberty University convocation Jan. 18 in Lynchburg, Va. (Drew Angerer/Bloomberg)

A nondescript office building on the north end of Washington Street in Old Town Alexandria is officially operating as the Donald Trump campaign’s Washington-area headquarters, with several senior aides spotted entering its tree-shrouded entrance on Monday.

Monday morning marked the first time the new space was used for a gathering of high-ranking staffers, according to several Trump associates. This particular meeting was about delegate strategy and planning for state conventions in the Republican presidential race, the associates said.

Among the Trump advisers at the Alexandria outpost Monday were Rick Wiley, a veteran operative with deep roots in the GOP establishment who joined Trump’s campaign this month as its national political director, deputy campaign manager Michael Glassner and Ken McKay, the former campaign manager for New Jersey Gov. Chris Christie who was announced Monday as a new senior adviser.

Few of the business people in dark suits and mothers with infants lined up Monday at the site’s bustling Starbucks noticed the arrival of the Republican front-runner’s campaign to the brick-and-glass office complex, called Washington Square, which features a Trader Joe’s grocery, a Talbots and a FedEx store.

The Trump staffers arrived and left without any formal announcement or opening, a reflection of the low-key nature of the campaign’s operation in Washington, which is focused on building relationships in Congress and managing state and convention efforts from afar rather than giving out literature or hosting events.

Previous huddles of Trump’s Washington-based advisers have for months been held at restaurants in Northern Virginia and on Capitol Hill, at Trump’s under-construction hotel on Pennsylvania Avenue, and at Trump supporter Ben Carson’s former campaign headquarters near the King Street-Old Town Metro station.

But as the billionaire’s campaign has expanded its once- small staff and prepares for a potential general-election contest, finding a larger facility to accommodate the new hires made by Trump confidant and strategist Paul Manafort has become a priority. The rental agreement on the property has been finalized in recent weeks, according to a person briefed on the arrangement.

Saul Centers, the real estate trust that operates the building, declined to comment or confirm its newest tenant when reached by phone on Monday.

According to the company’s website, Washington Square is advertised as having “three-story atrium lobbies, fitness center, concierge service, 600-space parking structure and computerized energy system.”

Manafort, who has an apartment at Trump Tower in New York — the campaign’s headquarters — also has a home near the new campaign office in Alexandria. Other top Trump advisers, such as Ed Brookover, have long lived and worked in the Alexandria area.