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The Pentagon is moving to prepare options for President Trump’s desired military parade, but it’s still not clear when, where or if it will ever happen.

The Washington Post reported Tuesday that, during a Jan. 18 meeting at the Pentagon, Trump requested options for an elaborate parade. The request came after Trump publicly and privately expressed admiration for a parade along the lines of France’s Bastille Day celebration, in which French troops march down the renowned Avenue des Champs-Elysees accompanied by tanks, personnel carriers and other armored vehicles.

Defense Secretary Jim Mattis acknowledged Wednesday that the Pentagon is drawing up options, linking the request to Trump’s affection for the military. But Pentagon officials have been hesitant to say much else, and various critics have suggested that it’s a bad idea. They include Navy SEAL veteran Robert O’Neill, who is credited with killing Osama bin Laden and is friendly with the president.

O’Neill tweeted Thursday that a “military parade is third world bulls—” that is out of place here.

“We prepare. We deter. We fight,” the tweet said. “Stop this conversation.”

Here are a few questions about what the options the Pentagon will present to the president could look like:

How large could the parade be?
The U.S. military regularly participates in parades and other public events all over the country, sometimes at great expense. But a point of friction with Trump’s idea is that it must be like France’s national parade, or even larger.

The United States has not staged anything comparable since 1991, when President George H.W. Bush presided over a national celebration of victory in the Persian Gulf War. About 8,800 U.S. troops marched, tanks and other armored vehicles rolled through Washington, and numerous aircraft flew overhead. It cost between $8 million and $12 million, according media reports at the time.

If the Pentagon carries out something comparable now, it would come at a time when Mattis and senior U.S. military officers regularly decry the disrepair that some military equipment is in after more than 16 years of war. But the military could conceivably offer options to the White House that are less extravagant, but still viewed as patriotic and impressive.

Who’s in charge?
Dana White, a Pentagon spokeswoman appointed by the Trump administration, told reporters Thursday that the Army has been put in charge of putting options together for the White House. The service is the U.S. military’s largest and includes the 3rd Infantry Regiment, a unit more commonly known as the “Old Guard,” which performs in ceremonial events at Arlington National Cemetery.

Where will it be?
Trump has often expressed his desire to have a parade down Pennsylvania Avenue, presumably on the same route from the Capitol to the White House that also passes the Trump International Hotel. But that is not necessarily a sure thing. National military parades were held in New York after World War I and World War II.

The parade also may not necessarily travel down Pennsylvania Avenue if it is held in the nation’s capital. In 1991, the marchers and equipment paraded down Constitution Avenue, along the National Mall.

White, asked Thursday where the parade would be held, would not say.

“We are looking at several different options,” she said. “We’re still in the nascent stages. When we have those options, we will provide that to the White House, and the president will decide.”

Why so many concerns about the damage?
Local officials in Washington have raised concerns about what kind of damage the parade could cause if 70-ton tanks and other armored vehicles are involved. That stems from a lesson learned after the 1991 celebration, after which roads needed to be repaved.

“We would always be concerned about the impact on the city, the impact on safety, the impact on pulling personnel, the impact on our roadways, and quite frankly, the attention it would attract,” Mayor Muriel E. Bowser, a Democrat, said Wednesday. “Usually when you see big military parades, it’s celebrating an end of a war, and I don’t think that’s been announced.”

What kind of logistics would it require?
It depends entirely on how large the president thinks the parade needs to be.

At its grandest, a parade in Washington would likely require the military to ship some equipment hundreds of miles from installations such as Camp Lejeune or Fort Bragg in North Carolina, the closest locations where some kinds of armored vehicles are based. The heaviest equipment, such as tanks, would probably be sent by rail.

Nearby installations also could be called upon to furnish equipment and service members to participate. They include Marine Corps Base Quantico and Fort Belvoir in Virginia and Joint Base Andrews in Maryland. The Pentagon also could seek help from National Guard units, which are distributed across the region.