Mitt Romney has been barred from a major conservative conference after he voted to hear from additional witnesses in Donald Trump’s impeachment trial.

The senator and former presidential nominee was one of only two Republicans who sided with Democrats by voting to hear new evidence against the president on Friday.

In response to Mr Romney's decision, Matt Schlapp, chair of the American Conservative Union, wrote on Twitter: “BREAKING: The 'extreme conservative' and Junior Senator from the great state of Utah, @SenatorRomney is formally NOT invited to #CPAC2020.”

CPAC is an annual political conference for conservative activists and politicians, which has featured appearances from Republican presidents such as Mr Trump, George W Bush and Ronald Reagan.

Despite Mr Romney’s efforts, the Republican-controlled Senate voted by 51-49 to block a push by Democrats to hear testimony from new witnesses, such as former national security adviser John Bolton.

All the president's lawyers: The team fighting Trump's impeachment Show all 6 1 /6 All the president's lawyers: The team fighting Trump's impeachment All the president's lawyers: The team fighting Trump's impeachment Alan Dershowitz Dershowitz is a controversial American lawyer best known for the high-profile clients he has successfully defended. Those clients have included OJ Simpson, Jeffrey Epstein and Harvey Weinstein. One longtime Harvard Law associated told the New Yorker Dershowitz "revels in taking positions that ultimately are not just controversial but pretty close to indefensible." Getty All the president's lawyers: The team fighting Trump's impeachment Ken Starr Starr became a household name in the 1990s as the independent counsel who led the investigation that led to Bill Clinton's impeachment. That investigation began as a look into a real estate scandal known as Whitewater, and eventually led to impeachment after Mr Clinton lied under oath about having an affair with White House intern Monica Lewinsky. AP All the president's lawyers: The team fighting Trump's impeachment Jay Sekulow Sekulow is the president's longtime personal attorney, and, now, personal lawyer in the White House. He has been accused by former Rudy Giuliani associate Lev Parnas of being "in the loop" during the Ukraine scandal. Getty All the president's lawyers: The team fighting Trump's impeachment Pam Bondi Bondi is the former attorney general in Florida, and a longtime backer of the president's. She made a name for herself in Florida for taking hyper partisan stances on issues, and her penchant for publicity. She is likely to be a prominent public-facing figure during the trial. AFP/Getty All the president's lawyers: The team fighting Trump's impeachment Pat Cipollone Cipollone is the White House counsel, and leading the president's defence team. Getty All the president's lawyers: The team fighting Trump's impeachment Rudy Giuliani While not officially named as one of the president's impeachment lawyers, it is hard to ignore Giuliani's outsized role in this process. The former mayor of New York has been making headlines for months as he defends his client, and for his apparent role in the effort to compel Ukraine to launch the investigation into Joe Biden. We'll see how he figures in the actual trial, which he has said he would like to be a part of. Reuters

Mr Bolton is thought to have first-hand knowledge of Mr Trump’s efforts to pressure Ukraine into announcing an investigation into his 2020 election rival Joe Biden.

In a manuscript for his upcoming book, the former national security advisor alleged that Mr Trump linked freezing military aid to Ukraine with forcing an investigation into Mr Biden.

With no new witnesses, it is almost certain the president, who has denied wrongdoing, will be acquitted next week.

Mr Romney has previously been a favourite of CPAC attendees and holds the record for winning the most CPAC straw polls for the most popular potential presidential candidate among conservative activists.

The senator has not yet commented on the decision and it is unclear if he was planning on attending the conference this year.

Michael Steele, a former chair of the Republican National Committee, described the decision to not invite the Republican senator to the conference as “embarrassing, stupid and juvenile”.

Soon after Mr Schlapp’s tweet, Mike Lee, Utah’s other Republican senator, tweeted in support of Mr Romney.

“Mitt Romney is a good friend and an excellent Senator. We have disagreed about a lot in this trial,” Mr Lee wrote.

“But he has my respect for the thoughtfulness, integrity, and guts he has shown throughout this process.”

The speakers at CPAC 2020, which will take place from 26-29 February, will include Nigel Farage, senior Republican Devin Nunes and Eduardo Bolsonaro, the son of Brazilian president Jair Bolsonaro.