Taylor arrives in Capitol to discuss Ukraine affair

The top U.S. diplomat in Ukraine arrived in the Capitol Tuesday morning to be interviewed as part of the Democrats' fast-advancing impeachment investigation, the latest in a string of witnesses to testify on President TrumpDonald John TrumpSchiff pleads to Senate GOP: 'Right matters. And the truth matters.' Anita Hill to Iowa crowd: 'Statute of limitations' for Biden apology is 'up' Sen. Van Hollen releases documents from GAO investigation MORE's dealings with Kiev.

William Taylor, the U.S. chargé d'affaires of Ukraine, had expressed concerns last month that Trump had crossed a line by threatening to withhold U.S. military aid to Ukraine to pressure the country's president, Volodymyr Zelensky, for political favors.

Taylor entered the Capitol just before 9:30 a.m. and was escorted to the secure meeting room, three floors below ground, where the House Intelligence Committee — joined by the Oversight and Reform and Foreign Affairs panels — are leading the investigation into allegations that Trump enlisted foreign help to boost his reelection chances next year.

Taylor did not comment as he passed reporters on his way to the room.

A career diplomat who has worked under numerous presidents of both parties, Taylor last month had warned several State Department colleagues of a "nightmare scenario" if it came to light that Trump and his allies — notably his personal lawyer Rudy GiulianiRudy GiulianiSchiff pleads to Senate GOP: 'Right matters. And the truth matters.' Schiff tells Senate Ukraine interference conspiracy was 'brought to you by the Kremlin' The Hill's Morning Report - House prosecutes Trump as 'lawless,' 'corrupt' MORE — had dangled the military aid to pressure Zelensky to find dirt on the president's political opponents.

In a Sept. 8 text to Kurt VolkerKurt VolkerGOP rejects effort to compel documents on delayed Ukraine aid GOP chairmen seek interview with Obama officials as part of Biden-Ukraine probe Push to investigate Bidens sets up potential for Senate turf war MORE, former special envoy to Ukraine, and Gordon Sondland, U.S. ambassador to the European Union, Taylor worried that Ukraine would make good on providing an unspecified "interview," but Trump would renege on the military aid.

"The nightmare is they give the interview and don't get the security assistance," Taylor texted to Volker and Sondland, according to the transcripts provided to Congress by Volker earlier in the month. "The Russians love it. (And I quit)."

The next day, Taylor warned Sondland that "it's crazy to withhold security assistance for help with a political campaign."

Sondland, a wealthy hotel magnate and Trump donor with no previous diplomatic experience, pushed back, saying Taylor was "incorrect" in surmising Trump's intentions.

"The president has been crystal clear no quid pro quo's of any kind," Sondland wrote.

An official working on the impeachment inquiry said the House Intelligence Committee subpoenaed Taylor this morning after the State Department allegedly sought to "direct" the diplomat "not to appear for his scheduled deposition," or seek to limit his testimony.

"As is required of him, Ambassador Taylor is now complying with the subpoena and answering questions from both Democratic and Republican Members and staff," the official said.

Both Volker and Sondland have already testified as part of the impeachment investigation, as has Marie Yovanovitch, the former U.S. ambassador to Ukraine who was removed in May after voicing concerns over Giuliani's pressure campaign.

Taylor is the most recent witness to testify in the Democrats' month-old impeachment inquiry, which was formally launched by Speaker Nancy PelosiNancy PelosiDemocrats hammer abuse of power charge, allege Trump put self over country Overnight Energy: Trump issues rule replacing Obama-era waterway protections | Pelosi slams new rule as 'an outrageous assault' | Trump water policy exposes sharp divides Pelosi slams Trump administration's new water rule: 'An outrageous assault' MORE (D-Calif.) in response to allegations from a government whistleblower that Trump had dangled almost $400 million in military aid to Ukraine if Zelensky would investigate the son of Joe BidenJoe BidenSchiff pleads to Senate GOP: 'Right matters. And the truth matters.' Anita Hill to Iowa crowd: 'Statute of limitations' for Biden apology is 'up' Sen. Van Hollen releases documents from GAO investigation MORE, a leading 2020 presidential contender.

The White House has said it will refuse to cooperate in the investigation, saying it's illegitimate. But Democrats have issued numerous subpoenas to break the stonewalling, and Taylor is just the latest witness to defy the administration's attempted blockade.

Trump has minced no words in his criticism of the ongoing inquiry, accusing Democrats of conducting a "witch hunt" designed with the sole purpose of sinking his reelection. Tuesday morning, just before Taylor arrived, Trump called the process "a lynching."  

"So some day, if a Democrat becomes President and the Republicans win the House, even by a tiny margin, they can impeach the President, without due process or fairness or any legal rights," he tweeted. "All Republicans must remember what they are witnessing here - a lynching. But we will WIN!"

Democrats have long condemned Trump's frequent race-based allusions, and wasted no time rebuking the president for his latest comments.

"Whenever his back is against the wall, a racial bomb is what we know him to [throw]," Rep. Karen BassKaren Ruth BassOmar calls on US to investigate Turkey over possible war crimes in Syria McConnell takes heat from all sides on impeachment Sunday Talk Shows: Lawmakers look ahead to House vote on articles of impeachment, Senate trial MORE (D-Calif.), head of the Congressional Black Caucus, said Tuesday morning.

Olivia Beavers contributed.