Here are some possible avenues regulators could pursue:
Unfair competition. If Amazon is vulnerable to antitrust law, it will be because regulators are changing the way they interpret antitrust law, said Lina Khan, who published "Amazon's Antitrust Paradox" in the Yale Law Journal in January.
Amazon wouldn't be punished for price gouging, since it generally pursues low prices at the expense of profits. Instead, it would be attacked for pushing other competitors out of the market.
"It's definitely true that you don't want antitrust to be used in protectionist ways," Khan said. "But it's also true that you can't have competition without competitors."
Favoring its own products. The Trump administration could enforce antitrust laws by suing Amazon "for using its platform and algorithms in a biased manner that prioritizes Amazon's own products and services over those of merchants that are dependent on Amazon's platform and with whom Amazon competes," according to a December 2016 paper published by The Capitol Forum, a news and analysis service that focuses on how policy affects market competition. (This would be similar to how the European Union went after Google.)
"It only takes one enforcement action covering a narrow instance of Amazon employing such bias to create precedent that could put its business model — leveraging its platform to vertically integrate into a wide range of industries — at risk," according to the analysis.
Acquisitions. Amazon may also take a more cautionary approach toward future acquisitions if it knows it's being watched by both Trump and regulators, Kovacic said. Amazon bought doorbell-maker Ring for about $1 billion in February and acquired Whole Foods for $13.7 billion last year.
Still, the DOJ should operate independently from the president on decisions to block deals. Hylton believes Amazon's Whole Foods acquisition would be approved today, just as it was last year.
Regardless, bringing a "giant monopolization case" against Amazon would be foolish unless the agencies had reams of evidence to back up a case, Kovacic said. That's not going to be affected by Trump one way or another, he said.
"There's no question being in the spotlight makes companies more cautious," Kovacic said. "But bringing a case against Amazon won't be easy. Most antitrust professionals, when pushed to do something that would not be sustainable, say 'check, please' and head for the exit."