WASHINGTON (NewsNation Now) — President Donald Trump worked Sunday to take back an apparent acknowledgement that Joe Biden won the White House and was making clear he would keep trying to overturn the election result.

President Donald Trump tweeted “I WON THE ELECTION!” Sunday evening.

On Sunday morning, he appeared to acknowledge for the first time that Joe Biden won the White House, but said he would not concede.

“He won because the Election was Rigged. NO VOTE WATCHERS OR OBSERVERS allowed, vote tabulated by a Radical Left privately owned company, Dominion, with a bad reputation & bum equipment that couldn’t even qualify for Texas (which I won by a lot!), the Fake & Silent Media, & more!,” Trump tweeted.

The Cybersecurity & Infrastructure Security Agency, a federal agency that oversees U.S. election security, said in a statement last week that the “November 3rd election was the most secure in American history.” The agency said, ”There is no evidence that any voting system deleted or lost votes, changed votes, or was in any way compromised.”

More than a week after Election Day, Trump has neither called Biden nor made a formal concession, and White House officials have insisted that they are preparing for a second term.

Trump continued to tweet about his plan to challenge the election Sunday.

Twitter soon posted warning labels about the tweets.

Of the nearly dozen lawsuits filed in Pennsylvania, Michigan, Georgia, Arizona and Nevada, the allegations made by the Trump Campaign range from election observers being denied access, to legitimate ballots rejected, to late or invalid ballots improperly counted, to poll workers coaching voters to vote Biden.

Some are still pending, however, many have been dismissed for lack of evidence.

Joe Biden defeated Trump to become the 46th president of the United States, according to the Associated Press. Biden won a trio of Midwestern battleground states: Michigan, Wisconsin and Pennsylvania, and topped the 270 electoral vote threshold to clinch the presidency. Biden so far has 77.5 million votes, the most ever by a winning candidate, to Trump’s 72.3 million.