According to The New York Times, Democratic Senator Richard Blumenthal of Connecticut sent a series of letters on Monday seeking information from people who were invited to an exclusive White House dinner back in October for donors to the project.

The senator asked the donors, who reportedly gave $2.5 million or more to the project, "what promises may have been or may yet be made in exchange for what presumably will be substantial contributions."

Blumenthal also sent a letter to an architect who was recently hired for the project, requesting design plans and cost estimates.

He further argued the project has become a "growing concern" among the American people, who are "entitled to all the relevant facts about the most substantial renovation of the White House in recent history."

Trump first announced the project back in July. At the time, he claimed it would cost $200 million, would not affect the White House, and would be entirely funded by contributions from wealthy donors.

But just a few months later, construction began with the demolition of the East Wing, and last week, Trump revealed that the estimate had ballooned to $400 million – double the initial price tag.

In October, Trump fired all members of the Commission of Fine Arts, the independent federal agency that reviews construction work in DC, thus avoiding potential challenges to his renovations.