Washington DC - Donald Trump will take a lap of honor at an IndyCar race through the streets of Washington this weekend, capping a summer of 250th anniversary festivities that the president has centered on himself.

Racing cars will roar past historic landmarks, including the US Capitol and Smithsonian Museums, as 25 drivers make 147 laps of the course at speeds of up to 185 mph.

Workers have had to weld down more than 200 manhole covers on the 250-mile circuit so that the sheer force created by the speeding cars doesn't tear them off.

Practice and qualifying sessions are on Saturday, and the Freedom 250 Grand Prix itself will take place on Sunday.

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Trump (80) is expected to take a ceremonial lap of honor in his armored limousine dubbed "The Beast" and then wave the green flag to start the race.

The event is being managed by the organizers of the IndyCar championship, the US motorsport whose cars resemble Formula One vehicles but often compete on oval tracks, including at the flagship Indianapolis 500 race.

It marks a final attempt by Trump to stamp his mark on Washington's celebrations of the 250th anniversary, which began with an Ultimate Fighting Championship bout in a huge cage on the White House lawn in June.

As with the UFC fight, the IndyCar organizers are footing the bill for a huge logistical challenge which has shut down some of Washington's busiest roads for days.

Thousands of spectators will line the route for the unprecedented race, which echoes Formula One contests staged on city streets in Las Vegas, Monaco, and Singapore.

Security will be tight with all spectators passing through metal detectors. Trump has escaped a number of alleged assassination attempts, including when a gunman stormed the White House Correspondents' Dinner in April.

Trump has put himself at the center of the celebrations to honor the signing of the Declaration of Independence on July 4, 1776, which marked the split of the original 13 American colonies from Britain.

He has also attempted to leave his mark on Washington itself, starting construction on a huge ballroom at the White House, renaming institutions after himself and launching a troubled repainting of the Reflecting Pool on the National Mall.

But instead of being a unifying event, America's 250th birthday has largely sparked discord.

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In a speech at Mount Rushmore on July 3, Trump launched a blistering attack on Democrats and said the country was under threat from a "communist menace."

Trump then made himself the star of a major Fourth of July concert in Washington after a number of musical artists had dropped out, complaining that the event was becoming too political.

The former reality TV star capped the evening with flyovers by military jets followed by a world record firework display featuring 850,000 rockets in 40 minutes.

Polls meanwhile show Trump is deeply unpopular a year and a half after returning to the White House, with the Iran war and the cost of living driving his approval levels down.

Trump's approval rating has fallen to 33%, according to a Reuters/Ipsos poll conducted last week, the lowest of his current term.