Anthem Inc. drew the battle lines Monday in defense of itsproposed purchase of Cigna Corp., faulting the U.S. JusticeDepartment for refusing to see any benefit in the $48 billion dealas the blockbuster megamerger trial opened in Washington federaldistrict court.

Related: Anthem, Cigna accuse one anoher of mergerbreach

In his opening statement, Anthem lawyer Christopher Curran ofWhite & Case sought to discredit the government’s claim thatthe combination of the two health insurers would eliminatecompetition that has lowered prices, improved care and driveninnovation.

A combined Anthem and Cigna, Curran said, would better positionthe company to compete against the market leader, UnitedHealthGroup Inc., and against Aetna Inc., whose planned $37 billionacquisition of Humana Inc. goes to court in Washington on Dec.5.

Related: Health care mergers should be blocked,says AMA

The Justice Department has alleged, in part, that Anthem’sacquisition of Cigna would hurt competition for millions ofconsumers who receive health insurance from large nationalemployers. Antitrust enforcers sued in July to block the deal.

Curran argued Monday that large companies have the resources andsophistication to negotiate lower prices and even stitch together anetwork of competing insurers.

“The notion that these Fortune 500 companies will be victimizedhere is not realistic,” he said. Curran added: “It’s a menuselection that these companies make. There’s a variety ofalternatives.”

The trial, rooted in millions of documents in discovery and morethan 100 depositions, is expected to last through December.

Anthem, Cigna tension

In the buildup to trial, U.S. District Judge Amy Berman Jacksonwas struck by the reported discord between Anthem and Cigna. Thecompanies have accused each other of breaching the terms of theirdeal.

At one hearing, Charles Rule, a Paul, Weiss, Rifkind, Wharton& Garrison antitrust partner representing Cigna, asked forpermission to object to questions from Anthem. Jackson called therequest “completely extraordinary.”

Curran addressed the contentiousness in court Monday, sayingthat disputes over of the corporate governance of the combinedinsurer “should not impede their ability to integrate.”

Justice Department attorney Jon Jacobs noted that even the twohealth insurers’ chief executives have raised questions aboutwhether the combined company would be able to effectively wield itsnew negotiating power with providers.

“No one knows how these negotiations are going to wind up,because they are negotiations,” Jacobs said in court.

“It is Anthem’s burden to quantify efficiencies, and they won’tbe able to,” he added.

At what he called an “important time in the industry,” Jacobsargued the Anthem-Cigna deal would deprive the market ofcompetition that drives innovation.

“A key question in this is going to be: What creates innovation?Well, a broker in California answered that question in hisdeposition: Competition creates innovation,” Jacobs said.

“We’ll show that Cigna has innovated precisely because it is notthe wolf at the top of the hill in the vast majority of thesemarkets.”

Anthem, facing an April 30 deadline to close its acquisition ofCigna, pushed for a ruling from Jackson by the end of the year,giving the company time to secure approval from stateregulators.

Jackson effectively denied that request when she set Nov. 21 forthe start of trial. Jackson said she hopes to rule on the deal bythe end of January.

The trial will be divided into two parts—focusing first on thedeal’s effect on national markets, and then on local markets.Jackson said in September she might issue a preliminary rulingafter the first phase.

The Trump effect

President-elect Donald Trump didn’t articulate a clear antitrustposition on the campaign trail, although he said he would block AT&TInc.’s planned $85 billion purchase of Time WarnerInc.

Trump’s pick for U.S. attorney general, Republican Sen.Jeff Sessions of Alabama, does not have a clear record ofantitrust positions.

Trump’s Justice Department would likely have a chance to overseeany appeal in the case in the early months of his presidency.

One possible clue to Trump’s thinking on antitrust was ondisplay this month in a New York Times piece from Joshua Wright, aformer Federal Trade Commissioner who’sreportedly advising the Trump transition team on antitrustmatters. Wright argued that “big” isn’t inherently “bad.”

“The new antimerger fervor is based upon the presumption thatthey are never a good deal for consumers because more consolidationalways leads to higher prices, and never leads to cost savings orproduct improvements that benefit consumers,” Wright wrote.“Both are demonstrably false.”