WASHINGTON, March 18 (Xinhua) -- Republican lawmakers warned U.S. President Donald Trump on Sunday not to fire Special Counsel Robert Mueller, after Trump targeted the investigations into Russian meddling in the 2016 presidential election.

Trump lashed out at Mueller by name and questioned the biases of Mueller's investigation team in a series of tweets over the weekend.

In reaction, GOP lawmakers sought to defend Mueller and warn the Republican president to let the investigation team do their job.

AshLee Strong, a spokeswoman for House Speaker Paul Ryan, said in a statement that "as the speaker has always said, Mr. Mueller and his team should be able to do their job."

"If he tried to do that (fire Mueller), that would be the beginning of the end of his presidency," Senator Jeff Flake said on CNN's "State of the Union."

Trump began his Sunday by criticizing Mueller with harsh words on Twitter.

"Why does the Mueller team have 13 hardened Democrats, some big Crooked Hillary supporters, and Zero Republicans?" Trump tweeted Sunday.

"And yet, there is NO COLLUSION!" he added.

On Saturday, Trump tweeted "The Mueller probe should never have been started in that there was no collusion and there was no crime."

"It was based on fraudulent activities and a Fake Dossier paid for by Crooked Hillary and the DNC (Democratic National Committee), and improperly used in FISA COURT (U.S. federal court established and authorized under the Foreign Intelligence Surveillance Act) for surveillance of my campaign. WITCH HUNT!" Trump tweeted.