Trump calls for impeachment of Republican Senator Romney

US President Donald Trump on Saturday called for the impeachment of his bitter critic and prominent Republican Senator Mitt Romney, using a hashtag on Twitter in all capital letters.

"I'm hearing that the Great People of Utah are considering their vote for their Pompous Senator, Mitt Romney, to be a big mistake. I agree! He is a fool who is playing right into the hands of the Do Nothing Democrats! #IMPEACHMITTROMNEY," Trump tweeted.

Trump's tweet came a day after Senator Romney, who during the 2016 presidential elections had called the president a "con artist", criticised him for his handling of the Ukrainian issue.

"Not only are the Do Nothing Democrats interfering in the 2020 Election, but they are continuing to interfere in the 2016 Election. They must be stopped!" he said in another tweet.

In a third tweet, Trump said that Romney's time was up.

"Mitt, get off the stage, you've had your turn (twice)!" Trump tweeted along with a news video of Romney, who was the Republican presidential nominee in 2012.

Romney has had a troubled relationship with Trump. When the Utah Senator made his second bid for the White House in 2012, Trump endorsed him and called him more "presidential" than Barack Obama. But after Romney lost the election, Trump criticised him for his defeat.

On Friday, Romney had slammed Trump for asking China and Ukraine to investigate former Vice President Joe Biden.

"By all appearances, the President's brazen and unprecedented appeal to China and to Ukraine to investigate Joe Biden is wrong and appalling," Romney tweeted.

"When the only American citizen President Trump singles out for China's investigation is his political opponent in the midst of the Democratic nomination process, it strains credulity to suggest that it is anything other than politically motivated," he tweeted.