Oleksii Liskonih/iStock(WASHINGTON) -- It was an exclusive dinner held amid the Greek columns of the Mellon auditorium in Washington, D.C., celebrating the inauguration of the incoming president, Donald J. Trump. The guest list included close friends of the president-elect, high-ranking campaign aides and an array of foreign ambassadors and dignitaries, along with some hoping to one day hold a coveted post in the nation’s diplomatic corps.

For some of those attendees, getting access to this elite club required the same as gaining entrée to Washington’s other power clubs: a large check. That’s how hotelier Gordon Sondland found his way into this dinner that included entertainment by casino mogul and Trump pal Steve Wynn, who flew in Las Vegas showgirls to perform a Broadway-style rendition of Frank Sinatra’s “New York, New York.”

Sondland would eventually secure the role of U.S. Ambassador to the European Union, a much-sought-after post in Brussels – a long way for this Seattle/Portland-based hotel mogul with limited diplomatic experience. Sondland is not the first ambassador in the GOP or Democrat administration to get plum assignment out of patronage, but the top spot for U.S. mission to the E.U. has typically been reserved for technocrats with an extensive diplomatic expertise.

Sondland was among the biggest donors to the Trump inaugural committee, writing a series of six-figure checks totaling $1 million under the name of multiple companies linked to himself and his wife Katherine Durant, according to campaign finance records.

The ambassador is now at the center of a congressional impeachment inquiry into President Trump. He has been requested by House Democrats to meet for a closed door deposition about his role in working with State Department colleagues helping Trump’s allies encourage Ukrainian officials to investigate former Vice President Joe Biden.

In a series of text messages that Sondland exchanged with former U.S Special Envoy to Ukraine Kurt Volker and Bill Taylor, the top U.S. diplomat to Ukraine, the three are seen over a series of days speaking about an investigation being pushed by president Trump’s personal attorney, Rudy Giuliani.

The exchange, provided to Congress by Volker, as part of his closed-door deposition before multiple House committees, shows what appears to be encrypted text messages regarding aid money Trump ordered to be held back from Ukraine.

In the Sept. 9 exchange, obtained by ABC News, the concerns are expressed by Taylor, a veteran of three administrations, who reiterates a previous warning.

“As I said on the phone. I think it's crazy to withhold security assistance for help with a political campaign.” Sondland, responding to Taylor, calls that "incorrect."

"Bill, I believe you are incorrect about President Trump's intentions. The President has been crystal clear: no quid pro quo’s of any kind. The President is trying to evaluate whether Ukraine is truly going to adopt the transparency and reforms that President Zelenskiy promised during his campaign," Sondland says.

Sondland then suggests to the group take the conversations offline, typing, “I suggest we stop the back and forth by text.” It’s unclear whether the material obtained by ABC News included the full exchange.

Now, House Democrats have asked Sondland to come up for a deposition next week.

Sondland's loyalty to Trump throughout the 2016 election cycle, however, was wavering at best.

In 2015, Sondland started out as early backer of Jeb Bush's presidential candidacy, donating $25,000 to a pro-Bush super PAC Right to Rise USA and another $2,700 to his campaign committee. After Trump was picked as the GOP nominee for the general election, however, Sondland's name appeared on a list of Trump bundlers distributed by the Republican National Committee in July 2016.

According to the Seattle Times and Willamette Week reporting at that time, Sondland was also slated to co-host a big fundraiser for the Trump Victory committee in Seattle in August 2016 but later backed out of the event after Trump's controversial remarks about the family of slain Army Capt. Humayun Khan, saying then-nominee Trump's positions "do not align with their personal beliefs and values."

Sondland and Durant, his wife, who also run a charitable foundation, have been prolific GOP donors who have donated nearly $1 million to various Republicans and party committees, including $60,000 to Mitt Romney's joint fundraising committee with the Republican Party and another $50,000 to a pro-Mitt Romney super PAC in 2012.

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