On Wednesday, Senator Elizabeth Warren of MA and Representative Pramila Jayapal of Washington issued letters demanding information about the T-Mobile executives' stays and whether Trump was informed of them.
The company previous year said it had also hired a lobbying firm linked to Corey Lewandowski, President Donald Trump's former campaign manager. At $640 million - or $0.75 per share - T-Mobile profits still came in ahead of analyst expectations.
But merger or not, T-Mobile's business has been respectably humming along.
In a letter to the FCC on Monday, Legere attempted to counter one of the main arguments against the merger - that as soon as T-Mobile absorbs Sprint, competition in the market will decrease and rates will go up.
Shares of T-Mobile were down 3.69 percent as of 4:04 p.m. ET on Tuesday, while shares of Sprint were down 6.09 percent.
In the letter, Legere calls out critics of the merger whom he says are "largely employed by Big Telco and Big Cable". "I want to reiterate unequivocally that prices will go down and customers will get more for less. Rather, our merger will ensure that American consumers will pay less and get more". He noted the merger has been approved by 15 of the required 19 state public utilities commissions and added that he and Sprint Executive Chairman Marcelo Claure look forward to speaking with lawmakers before a joint hearing on Capitol Hill next week.
But from another perspective, Clyburn's involvement with T-Mobile serves to inoculate the company from critics who argue the deal will be largely bad for consumers because it will mean the elimination of a competitor from the US wireless market.
But having served for almost a decade on the commission, Clyburn knows all the ins and outs of the agency and how it approaches merger reviews, making her experience invaluable to T-Mobile as it tries to persuade the FCC and the Justice Department to bless its acquisition. Together, the two companies could "to react, invest and compete harder and that will be good for consumers and innovation", he said.
Former FCC Commissioner Robert McDowell, a Republican, also consults for T-Mobile. "The New T-Mobile will be uniquely positioned to give you both".