[T-Mobile and Sprint attacked each other for years before they decided to team up.]
Mr. Legere made numerous visits to both the F.C.C. and the Justice Department, documenting his activity on social media. A month after the deal was announced, Mr. Claure was a host of a fund-raiser for Representative Marsha Blackburn, a Tennessee Republican who was running for Senate. Ms. Blackburn, a longtime supporter of the telecommunications industry, was elected to the Senate in November.
Several lawmakers expressed misgivings over Mr. Legere’s Washington visits, noting the dozens of times that he and other T-Mobile executives have stayed at the Trump International Hotel there. The companies have denied doing anything inappropriate to curry favor with federal officials.
If the deal is completed, it would be a victory for the billionaire entrepreneur Masayoshi Son, whose SoftBank investment group owns a controlling interest in Sprint, a company with debts of $40 billion. Mr. Son has been trying to unload the troubled carrier for years.
In December 2016, Mr. Son met with Mr. Trump, who was then the president-elect, at Trump Tower and pledged to invest some $50 billion in the United States in an initiative that would create 50,000 jobs. In February, SoftBank executives held discussions in Washington with members of the president’s economics team.
The Justice Department’s approval of the merger relies on the future actions of Dish, a company with a history of violations that is controlled by the billionaire Charles Ergen, an expert poker player and tough negotiator. Dish would face millions of dollars in fines if it failed to build out its cellular service, Mr. Delrahim said.
In a statement on Friday, Dish said it would voluntarily pay a fine of up to $2.2 billion if it failed to deploy a 5G network covering at least 70 percent of the country’s population in the next four years.
The Justice Department and the F.C.C. will monitor Dish to ensure that it adheres to the agreement, amounting to what is known as a behavioral remedy under which federal regulators watch over a for-profit business. In assessing previous merger deals, Mr. Delrahim has criticized such arrangements. On Friday, he said the agencies’ oversight of Dish did not amount to a behavioral remedy, largely because they will track Dish’s initial build-out of a wireless network and then step away after it starts operating.