Shares of Sprint jumped as much as 15% on Wednesday and shares of T-Mobile gained as much as 4%. Sprint sought to acquire T-Mobile in 2014, but antitrust regulators in the Obama administration indicated their opposition. The deal would have combined the third and fourth ranked wireless carriers, which regulators feared would reduce competition and lead to higher prices for consumers.

But ever since, Sprint CEO Marcelo Claure and Masayoshi Son, CEO of Sprint majority-owner Softbank Group, have repeatedly expressed their desire to revisit the deal if the election brought a new approach in the antitrust area.

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“We’ve always said that we were interested,” Claure told Fortune in August. “It would be nice to combine both companies to give us scale. Today that is a wish.”

Sprint (S) CFO Tarek Robbiati spoke on Wednesday at a Wells Fargo investor conference for half an hour, but was not asked about mergers or the incoming Trump administration.

Trump’s views on telecom mergers aren’t crystal clear. The president-elect said during the campaign that he opposed mergers such as AT&T’s (T) acquisition of Time Warner (TWX) because of excessive media consolidation. Trump has also said he would favor undoing Comcast’s (CMCSA) NBC Universal deal that was approved in 2011 under Obama.

But on telecom, some signs have pointed towards a more lenient approach. For the Federal Communications Commission, Trump’s transition team is relying on Jeffrey Eisenach, an old Washington hand with long experience making pro-telecom industry arguments, Politico reported last month. Eisenach is an economist who worked at the Federal Trade Commission during the Reagan administration. In recent years, as a fellow at the American Enterprise Institute, he has spoken out against the Obama FCC’s efforts to protect net neutrality.

Clearly, stock market investors think Trump would look more favorably on a potential Sprint-T-Mobile combination. But Sprint may not end up the winner even if it bids for T-Mobile.

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Such a move could spark a bidding war for T-Mobile, as other companies with much greater resources including Google (GOOGL), Comcast and Charter Communications (CHTR) have been mentioned more recently as possible suitors. T-Mobile CEO John Legere, who has more than doubled the carrier’s subscribers since he took over in late 2012, has also said he would drive a hard bargain with any would-be acquirer given his success.

With so many unknowns and potential scenarios in play, some of the optimism appeared to fade as the day wore on Wednesday. In late morning trading, Sprint shares were up 10% and T-Mobile gained 2%.