WASHINGTON – The U.S. State Department told a key witness not to appear before Congress, a senator called for Rudy Giuliani to testify and the White House told House Speaker Nancy Pelosi there would be no cooperation in what it called a “partisan” impeachment investigation against President Donald Trump.

All of this and more happened on Tuesday.

It all stems from the July 25 phone call in which Trump asked Ukraine President Volodymyr Zelensky to look into former Vice President Joe Biden and his son. A whistleblower complaint alleges Trump pressured Zelensky and also raised concerns about U.S. monetary aid that was delayed to Ukraine.

We've rounded up the most important developments from today on impeachment:

Sondland subpoenaed after Trump blocked him from appearing before Congress

Trump and the State Department blocked European Union Ambassador Gordon Sondland from appearing before a trio of congressional committees to answer questions about his role in pushing Ukraine's president to investigate Biden.

In response, House Democrats issued a subpoena, demanding he hand over key documents by Oct. 14 and appear before the panels on Oct. 16.

Sondland's attorney Robert Luskin said the State Department directed him not to cooperate with the probe or appear before lawmakers.

"Early this morning, the U.S. Department of State directed Ambassador Gordon Sondland not to appear today for his scheduled transcribed interview before the U.S. House of Representatives Joint Committee," Luskin said. He had originally said Sondland agreed to “appear voluntarily”.

Trump defended the decision to prevent Sondland's testimony, saying the Democrats' inquiry is illegitimate, claiming he would love "to send Ambassador Sondland" to testify, but he, unfortunately "would be testifying before a totally compromised kangaroo court."

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White House tells Pelosi that Trump will not participate in inquiry

In a letter released Tuesday, Trump and his team told Pelosi and other Democratic leaders that they will not provide documents or witnesses to House impeachment investigators because they consider the investigation to be unfair and illegitimate.

"You have designed and implemented your inquiry in a manner that violates fundamental fairness and constitutionally mandated due process," White House Counsel Pat Cipollone wrote in a blistering eight-page letter to Pelosi and the chairmen of three key House committees.

"President Trump cannot permit his Administration to participate in this partisan inquiry under these circumstances," Cipollone added, reiterating the GOP talking point that democrats are just seeking "to overturn the results of the 2016 election."

Some Democrats scoffed at Trump's objections and indicated they may go to court to try and enforce subpoenas and document requests.

House Democratic investigators subpoenaed Sondland minutes after the White House letter.

Pelosi released a statement, responding to Trump's letter: “The White House should be warned that continued efforts to hide the truth of the President’s abuse of power from the American people will be regarded as further evidence of obstruction."

“Mr. President, you are not above the law. You will be held accountable,” she concluded.

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Giuliani called to testify by Graham

Trump’s personal lawyer, Giuliani, was invited by Senate Judiciary Committee Chairman Lindsey Graham, R-S.C., to discuss what he learned during his investigation into Ukraine.

"Given the House of Representatives’ behavior, it is time for the Senate to inquire about corruption and other improprieties involving Ukraine," Graham tweeted. "Therefore I will offer to Mr. Giuliani the opportunity to come before the Senate Judiciary Committee to inform the Committee of his concerns."

California Sen. Dianne Feinstein, the ranking Democrat on the committee, embraced hearing from Giuliani, saying in a statement that she welcomes “the opportunity to question Rudy Giuliani under oath about his role in seeking the Ukrainian government’s assistance to investigate one of the president’s political rivals.”

Giuliani told The Washington Post he was "very interested" in Graham's offer, but "there are a lot of legal issues to consider."

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China tells Trump 'no' to investigating Biden

After Trump publicly said China should also investigate Biden and reports swirled that the political prospects of Biden and Sen. Elizabeth Warren were mentioned in a phone call between Trump and President Xi Jinping, China said no.

Last week, Trump told reporters on the White House South Lawn, "By the way, likewise, China should start an investigation into the Bidens because what happened in China is just about as bad as what happened with Ukraine.”

“We have no intention of intervening in the domestic affairs of the United States. Our position is consistent and clear," China foreign ministry spokesman Geng Shuang said in a report in the South China Morning Post, the main English-language newspaper in Hong Kong.

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Senate report concludes Russia helped Trump in 2016, calls for action for 2020

A new report released by the Senate Intelligence Committee on Russian interference in the 2016 election has concluded that Russia acted to boost Trump at the expense of Democratic nominee Hillary Clinton.

Among other controversial issues, Russia attempted to inflame tensions around race and "targeted African-Americans more than any other group or demographic," and according to the committee, the election interference efforts did not end with the 2016 election.

The report delivers a call for future action to prevent foreign election interference, saying that "the Executive Branch should, in the run up to the 2020 election, reinforce with the public the danger of attempted foreign interference in the 2020 election."

They also recommend the creation of an interagency task force to combat misinformation efforts and a public information campaign against foreign interference.

The report comes in the midst of Trump asking Ukraine and China to help him investigate, as well as previous reports that Trump asked multiple countries, including Australia, to help Attorney General William Barr's ongoing inquiry into the origins of special counsel Robert Mueller's examination of Russian interference in the 2016 election investigation.

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What's next?

The House Foreign Affairs, Intelligence and Oversight committees scheduled a deposition with Lev Parnas, a Ukrainian-born businessman who helped introduce Giuliani to a Ukrainian prosecutor who reportedly sought to provide dirt on Biden for Thursday.

On Friday, the three committees scheduled a deposition with Igor Fruman, a Ukrainian-born business partner who helped introduce Giuliani to the Ukrainian prosecutor and Marie Yovanovitch, a career diplomat and former U.S. ambassador to Ukraine. Trump called Yovanovitch "bad news" in his phone call with the Ukrainian president.

More:Trump impeachment investigation: Here is what's going on this week

Contributing: Bart Jansen, John Fritze, Michael Collins, David Jackson, Christal Hayes, Nicholas Wu, Jeanine Santucci, Deirdre Shesgreen, Kevin Johnson and Kristine Phillips, USA TODAY.