President Donald Trump’s first year in office was already shaping up to be a less-than-banner one for M&A. Now, the U.S. Justice Department’s lawsuit to block AT&T Inc.’s $85.4 billion takeover of Time Warner Inc. could put the brakes on future dealmaking too.

“I think this has put a wet blanket over consolidation around the whole space,” Christopher Marangi, co-chief investment officer of Gabelli Funds, said in a Bloomberg TV interview. “A lot of companies are going to be watching this case very closely.”

With just six weeks of 2017 to go, global M&A activity is about 12 percent lower than at the same time last year, with $2.4 trillion of deals announced — the lowest tally since 2013. U.S dealmaking is leading the slump, with activity almost a third lower than at this point in 2016, as companies and their advisers await certainty on tax reform and regulatory intervention.

The Justice Department’s lawsuit will give them some clarity on the latter. In attempting to block the deal, the Trump administration is moving in the opposite direction than many expected, with Republicans historically seen as more business — and therefore M&A — friendly.

Chief executive officers will also be closely watching AT&T’s approach to the courtroom battle. So far, CEO Randall Stephenson has been defiant in the face of the contest, saying the case “stretches the very idea of antitrust law beyond the breaking point.” It’s not the first time Stephenson has come up against government opposition to a mega deal: In 2011, AT&T pulled its $39 billion bid to acquire T-Mobile US Inc. after government opposition.

Before the lawsuit was announced, there were clear signs that dealmaking discussions (if not announced transactions) were heating up. Broadcom Inc.’s $105 billion offer for fellow chipmaker Qualcomm Inc. would be the biggest deal of 2017, and large media suitors are circling 21st Century Fox Inc. on the hunt for a multibillion-dollar package of media assets. Cross-border talks are active too: Nestle SA is considering a bid for U.S. organic food maker Hain Celestial Group Inc., people familiar with the matter said Monday.

With the Thanksgiving break looming in the U.S., dealmakers may decide that the AT&T lawsuit — and the increased scrutiny on large transactions that will come with it — are reason enough to down tools for a while. Even if they don’t, it’s unlikely that last-minute agreements will boost M&A volumes in 2017 within reach of the past few years. According to data compiled by Bloomberg, no period between Thanksgiving and year-end has yielded more than $350 billion in overall dealmaking for at least a decade.

“If AT&T is not allowed to buy Time Warner, what does that mean for Comcast’s intentions toward Fox, or other companies’ intentions toward Fox?” Marangi said