A trial in the landmark antitrust case against social media giant Meta kicks off in Washington on Monday.

The US competition and consumer watchdog alleges that Meta, which already owned Facebook, bought Instagram in 2012 and WhatsApp in 2014 to eliminate competition, effectively giving itself a monopoly.

The FTC reviewed and approved those acquisitions but committed to monitor the outcomes. If the Federal Trade Commission (FTC) wins the case it could force Meta CEO Mark Zuckerberg to sell off both Instagram and WhatsApp.

Meta previously said it was sure it would win and experts have told the BBC it is likely to argue that Instagram users have had a better experience since it was taken over.

"The [FTC's] argument is the acquisition of Instagram was a way of neutralizing this rising competitive threat to Facebook," says Rebecca Haw Allensworth, a professor of antitrust at Vanderbilt Law School.

Ms Allensworth says Mr Zuckerberg's own words, including those from his emails, may offer the most convincing evidence at trial.

"He said it's better to buy than to compete. It's hard to get more literal than that," Ms Allensworth says.

Meta, on the other hand, is likely to argue that intent is not particularly relevant in an antitrust case.

"They're going to say the real question is: are consumers better off as a result of this merger?," she said. "They'll put on a lot of evidence that Instagram became what it is today because it benefited from being owned by Facebook."

Mr Zuckerberg and the company's former chief operating officer Sheryl Sandberg are both expected to testify at the trial, which could run for several weeks.

The case, FTC v Meta, was filed during US President Donald Trump's first administration but risks becoming politicized during his second term.

Mr Zuckerberg has lobbied Trump in person to have the FTC drop the case, according to the Wall Street Journal.

When asked by the BBC to confirm that report, Meta sidestepped the question but said in a statement: "The FTC's lawsuits against Meta defies reality."

"More than 10 years after the FTC reviewed and cleared our acquisitions, the commission's action in this case sends the message that no deal is ever truly final," a Meta spokesperson told the BBC.

Relations between Mr Zuckerberg and Trump had been frosty partly because Trump was barred from Meta's social media platforms after the US Capitol riot in January 2021.

Since then, the relationship has thawed somewhat.

Meta contributed $1m (£764,400) to Trump's inaugural fund, and in January announced Ultimate Fighting Championship Fighter (UFC) boss Dana White, a close Trump ally, would join its board of directors.

The company also announced in January that it was doing away with independent fact-checkers.

President Trump's move to fire two FTC commissioners in March also hangs over the case.

As Democrats, Rebecca Kelly Slaughter and Alvaro Bedoya were in the minority on the five-seat commission.

Until Wednesday, just two seats of those seats were filled, both by Republicans. Another Republican was confirmed by the Senate on Thursday.

Slaughter and Bedoya - who are suing the Trump administration to be reinstated - say the move to push them out was meant to intimidate.

"The president sent a very clear signal not only to us but to Chairman Ferguson and Commissioner [Melissa] Holyoak that if they do something he doesn't like, he could fire them too," Slaughter told the BBC in a recent interview.

"So if they don't want to do a favor for his political allies, they're on the chopping block as well," Slaughter said.

Slaughter and Bedoya both expressed alarm at recent reports about Zuckerberg's lobbying efforts.

"My hope is that there is no political interference," Mr Bedoya told the BBC.

The FTC did not respond to a request for comment from the BBC.

Ferguson, who was appointed as FTC chair by Trump, recently told The Verge he would "obey lawful orders" when asked what he would do if the president directed him to drop a lawsuit like the one against Meta.

Ferguson added that he would be very surprised if anything like that ever happened.

The FTC is considered a key antitrust watchdog. In recent years, it has returned hundreds of millions of dollars to victims of fraud, in addition to passing laws that ban junk fees and subscription traps.

But as the Meta trial begins, it's among the many independent regulatory agencies that the administration seems keen to rein in.

Chair Ferguson is also recently quoted reaffirming his belief that independent regulatory bodies are "not good for democracy."

FTC v Meta begins as another major antitrust case - USA v Google - enters what's known as the remedies phase.

The Department of Justice won the first phase of that case last summer when Judge Amit Mehta found that Google holds a monopoly in online search, with a market share of around 90%.

Last month, the DOJ reiterated a demand made during the Biden administration that a court break up Google's search monopoly.

The FTC's case against Meta will be tougher to prove, says Laura Phillips-Sawyer, an associate professor of business law at the University of Georgia.

"I think they have a real uphill battle," Ms Phillips-Sawyer said of the FTC.

"They have a long road before any consideration of divestiture of Instagram or WhatsApp is considered."

That's because compared to online search, there's more competition in the personal network services space that Meta operates in, Ms Phillips-Sawyer said.

Meta in a statement said the evidence at trial "will show what every 17-year-old in the world knows: Instagram, Facebook and WhatsApp compete with Chinese-owned TikTok, YouTube, X, iMessage and many others."