Hillary Clinton and Bernie Sanders (Ian Thomas Jansen-Lonquist/Bloomberg)

The growing opposition to AT&T’s $85 billion bid to acquire Time Warner by populist politicians on the left and right offers a preview of the ideological fights that Hillary Clinton would immediately confront if she were elected president.

The merger, expected to go before antitrust regulators early next year, would be one of the first major tests of Clinton’s willingness as president to heed strident criticisms that the political system favors big businesses.

On Tuesday, Sen. Bernie Sanders said he would pressure Clinton to oppose the merger, if she won the White House.

“If Hillary Clinton is elected president we must do everything possible to make certain that her administration mounts a vigorous anti-trust effort,” he said in a statement to the Post. “We must reject the AT&T-Time Warner merger. We need more diverse media ownership, not less.”

Sen. Elizabeth Warren also on Tuesday called for rigorous oversight of the deal. Clinton’s rival, Donald Trump, has already said he would oppose it.

“There’s no question there’ll be a firestorm of protest from the Sanders-Warren wing of the Democratic party,” said Jeffrey Chester, executive director of the Center for Digital Democracy, “forcing Hillary to get tough on Wall Street with the first test case being AT&T-Time Warner.”

To persuade regulators to support the merger, AT&T is expected to bring the full weight of its lobbying machine to bear. The telecom giant operates one of the Washington’s most sophisticated operations, an outgrowth of its decades-long relationship with the government as a regulated monopoly.

The company ranked as the 13th-biggest spender on lobbying last year and maintains a stable of nearly 100 lobbyists who have sought to shape more than 50 pieces of federal legislation this year. It has donated nearly $66 million to politicians over the past two decades, largely to GOP candidates, according to the Center for Responsive Politics.

But this election cycle, Clinton is by far the largest beneficiary of donations made by AT&T employees, family members and a political action committee, according to the center. With nearly $200,000 collected so far, Clinton received more than twice as much money as Sanders and more than four times as much as Republican senator Ted Cruz, who represents Texas where AT&T is based. Trump has received about $17,000 from the company, according to the center.

AT&T’s Washington presence at times has given the company an advantage in regulatory battles. But this time, the company will be facing a far more skeptical Washington, influenced by an electorate that was already suspicious of corporate America and is now facing the largest tie-up since Comcast’s 2011 purchase of NBCUniversal.

Beyond Trump and Sanders, a bevy of lawmakers have been critical of the deal or called for rigorous oversight of the transaction, including Sens. Al Franken (D-Minn.), Chuck Grassley (R-Iowa), Amy Klobuchar (D-Minn.), Patrick Leahy (D-Vt.) and Mike Lee (R-Utah).

“You are seeing a convergence of opinion both from the left and the right that big is necessarily bad,” said Robert Cooper, an antitrust lawyer at the firm Boies, Schiller & Flexner, “and from both sides of the spectrum, there seems to be almost an instinctive condemnation now of something that looks like a very big deal.”

Clinton’s response to the mega-merger has so far been measured. Regulators should certainly examine the deal, her aides have said. Clinton’s running mate, Tim Kaine, told NBC Sunday that he held “concerns and questions” about the tie-up. But the Clinton campaign has stopped short of calling for the transaction’s demise. It did not immediately respond to a request for comment.

The AT&T-Time Warner deal would combine the country’s largest pay-TV provider — and second-largest wireless carrier — with a media titan controlling some of pop culture’s most recognizable brands, such as HBO, CNN and Warner Bros. The deal reflects the crumbling distinction between the once-segregated media and communications industries as Americans shift their content consumption to the Internet. And for the first time, it could put AT&T in direct competition with the likes of Netflix and Amazon.

The tie-up will likely be analyzed by the Justice Department, and possibly by the Federal Communications Commission, to ensure it will not damage economic competition or hurt consumers. As a condition of the deal, regulators could demand requirements of the combined company to hinder its ability to harm rivals. The people Clinton or Trump appoints to either agency at the start of a new administration would set the tone for the review of the deal.

"Once it gets into the hands of regulators, the professionals who do this thing for a living — the data and the law will dictate how this deal is handled," said AT&T chief executive Randall Stephenson, at a conference Tuesday.

And Clinton’s neutral answer on the deal may reflect an early indication of her strategy, said Gene Kimmelman, a former Justice Department antitrust official who is now president of the consumer group Public Knowledge. Although the Clinton campaign backs an aggressive antitrust enforcement regime, he said, its positions also appear to support using regulatory tools to shape corporate behavior.

“Everyone focuses on ‘Are you going to block it or not,’ but in most instances… antitrust is one tool among many,” said Kimmelman. “Regulatory interventions to promote competition are equally or even more important.”