President Trump is gearing up for his military-themed celebration on July Fourth, but the fireworks already are erupting as critics complain about the nature and cost of the event -- and authorities worry about possible violent clashes between leftist and right-wing protesters.

Anti-war Code Pink members began arriving at the Lincoln Memorial on Wednesday, saying in a press release they intended "to protest the militarization of July 4" and hold an "anti-imperialist festival" Thursday on the National Mall.

They were looking to float a “Baby Trump” balloon -- versions of which have been flown at protests in London -- blocks away from the national celebration. The National Park Service denied their initial request to fly the blimp, but Code Pink filed additional paperwork in a last-ditch bid to see the inflated caricature of the president take float.

The bid was rejected. “We are not allowed to fly the baby just keep him on the ground,” a Code Pink official said.

TANKS ARRIVE IN D.C. AS TRUMP CONFIRMS JULY FOURTH CELEBRATION WILL FEATURE MILITARY DISPLAY

But other left-wing activists organized by All Out D.C. are set to mobilize on Saturday in response to a planned rally by self-described “Western chauvinist” group the Proud Boys. U.S. Park Police, which covers the National Mall, is on alert, according to the Washington Post.

"We'll have people in different locations and watching," spokesperson Sgt. Eduardo Delgado told the Post. "We prepare for the worst and hope for the best."

The worst could be a repeat of what happened in Portland, Ore., last weekend, when Antifa members attacked conservative demonstrators including the Proud Boys.

PORTLAND POLICE RELEASE PHOTOS OF SUSPECTS IN VIOLENT ANTIFA CLASHES THAT INJURED CONSERVATIVE WRITER

Portland police said on Monday that a number people in the crowd concealed and brandished weapons, including "batons, projectiles, and firearms." A total of eight people were treated by medics, including three police officers, and three people were hospitalized, officials said.

One of the All Out D.C. organizers said no one on their side is looking to start a fight, but they will be ready for one.

"No one in Antifa or Black Lives Matter or any of the different affinity groups are looking to instigate something. We are looking to uplift and protect our community as one," Carlos Chavarría told the Post. "But we are prepared for them to try to start a fight with us, to come to our action and try to instigate something."

Trump's plans for Thursday, meanwhile, have drawn complaints over the potentially garish military display and the accompanying cost.

"There's going to be a big price tag for this and the taxpayers will have to pick up the tab," Senate Appropriations Committee member Chris Van Hollen, D-Md., said, according to NPR.

The exact cost of the event is unknown, but the Pentagon is sending a B-2 bomber for a flyover at a rate of $122,311 an hour. That's in addition to Navy F-35 and F-18 fighter jets, Army and Coast Guard helicopters, and Marine V-22 Ospreys. On top of that is an aerial show by the Navy's Blue Angels and appearances by Army Abrams tanks.

A U.S. official told Fox News that two tanks will be moved late Wednesday under the cover of darkness to the National Mall near the Lincoln Memorial.

Trump, who plans to break with tradition and speak at the festivities on Thursday, continues to defend the planning -- and downplay the costs.

"The cost of our great Salute to America tomorrow will be very little compared to what it is worth," Trump said in a Wednesday morning tweet. "We own the planes, we have the pilots, the airport is right next door (Andrews), all we need is the fuel." He said the fireworks that will be part of the celebration were donated.

According to multiple reports, however, the National Park Service is diverting almost $2.5 million for the occasion.

Trump's insistence on speaking at the event drew additional criticism. House Majority Leader Steny Hoyer, D-Md., has described Trump’s July Fourth celebration as “a political rally.”

Fox News' Travis Fedschun, David McAlpine, Lucas Tomlinson and The Associated Press contributed to this report.