WASHINGTON — Republicans pressed their offensive against the Democratic-led impeachment inquiry against President Donald Trump on Thursday with plans for a Senate resolution calling it illegitimate, while the White House lauded lawmakers in his party who stormed into a high-security room and interrupted testimony.

The House of Representatives is examining whether there are grounds to impeach Trump over his request in a July telephone call to Ukrainian President Volodymyr Zelenskiy to investigate a domestic political rival, Joe Biden. The former US vice president is a leading contender for the Democratic nomination to face Trump in the 2020 presidential election.

Trump on Monday called on his fellow Republicans to "get tougher" in fighting the impeachment inquiry, which threatens to end his presidency.

Republican Senator Lindsey Graham, a Trump ally who on Tuesday agreed with the president's description of the impeachment probe as a "lynching" by Democrats, was scheduled to announce his resolution later on Thursday. Graham's office said the resolution would condemn the "closed-door, illegitimate impeachment inquiry."

Republicans have sought to attack the legitimacy of the impeachment probe and have complained about depositions being given behind closed doors. The US Constitution, however, gives the House wide latitude in how to handle impeachment.

Even if passed in the Republican-led Senate, the resolution would not affect the House inquiry. However, it would place Republican senators on the record on impeachment at a time when some cracks in Trump's support within his own party have appeared, including pointed criticism from Senator Mitt Romney.

If the House passes articles of impeachment — formal charges — the Senate would then hold a trial on whether to remove Trump from office. A two-thirds majority of the 100-seat Republican-controlled Senate would be required to remove the president.

No US president has ever been removed from office via impeachment.

Senate Majority Leader Mitch McConnell voiced support for Graham's resolution but did not say when he would bring it up for a vote. He also accused House Speaker Nancy Pelosi and her fellow Democrats of having an "impeachment obsession."

Chuck Schumer, the top Senate Democrat, accused Trump and his Republican congressional allies of hypocrisy for demanding that impeachment proceedings be done in public even as the administration withholds subpoenaed documents and tries to block testimony to House investigators.

"One the one hand, you say you want everything to be public when it comes to the hearings. But you won't give up any documents," Schumer said on the Senate floor. "The hypocrisy, the self-serving nature of the president's statements and his Republican allies here in the House and Senate is glaring."

More than two dozen House Republicans barged into a high-security hearing room on Wednesday and delayed for several hours the testimony of a Pentagon official in the impeachment inquiry, complaining about a lack of transparency. Republican members of the three committees leading the House inquiry have taken part in the proceedings throughout.

"Thank you to House Republicans for being tough, smart, and understanding in detail the greatest Witch Hunt in American History. It has been going on since long before I even got Elected (the Insurance Policy!). A total Scam!" Trump wrote on Twitter.

"I'm glad they did it," White House spokeswoman Stephanie Grisham said of the House Republicans, speaking on Fox News.

Trump had withheld $391 million in security aid to Ukraine passed by Congress to help counter Russia-backed separatists in the eastern part of the country.

In testimony on Tuesday, William Taylor, the top US diplomat in Ukraine, said Trump had made the aid contingent on the Ukrainian president announcing he would investigate Biden, his son Hunter Biden's tenure on the board of a Ukrainian energy company, and a debunked conspiracy theory that Ukraine, and not Russia, meddled in the 2016 US presidential election.

During the call with Trump, Zelenskiy agreed to the investigations. The aid was later provided.

US election law prohibits candidates from accepting foreign help in an election.

The impeachment inquiry was launched after a person within the US intelligence community lodged a whistleblower complaint against Trump based on the call to Zelenskiy.

In remarks to journalists in Kansas, Secretary of State Mike Pompeo declined to answer a question about Taylor's testimony that the diplomat had sent Pompeo a cable on Aug. 29 expressing his concerns about the withholding of the aid to Ukraine.

"This inquiry will proceed. Congress will perform its oversight function, the State Department will continue to do all of the things that we're required to do under the law and the Constitution," Pompeo told the Wichita Eagle and the Kansas City Star.

"I hope that they'll proceed in a way that is transparent and fair. And then the inquiry will wrap up," Pompeo added.

Democrats controlling the impeachment inquiry have said they will hold public hearings in the coming weeks. They hope to complete the inquiry by the end of the year and are coalescing around two articles of impeachment: abuse of power and obstruction, lawmakers and aides said. — Reuters.