U.S. President Barack Obama gave his endorsement to Hillary Clinton's White House bid on Thursday. He asked Democrats to support her after the dispute with Bernie Sanders to get nominated for the party.

The presumptive Democratic nominee, Hillary Clinton, admitted that Obama's backing the Nov. 8 election "means the world" to her.

"I don't think there's ever been someone so qualified to hold this office," Obama said of Clinton in a video. "I'm with her. I am fired up, and I cannot wait to get out there and campaign for Hillary."

"It is absolutely a joy and an honor that President Obama and I over the years have gone from fierce competitors to true friends," Clinton told Reuters.

Obama still has strong approval ratings after his eight-year term in office. He will travel with Clinton on the campaign trail the following week in Wisconsin.

It also puts the heat on Sanders, the U.S. senator from Vermont, to leave the race and support Clinton so that the focus can now be on defeating Donald Trump, the Republican candidate.

The former first lady Clinton touched the required number of delegates to win the party nomination this week. She created history as the first woman candidate for the top U.S. position.

However, the inevitable slam came from Trump on Twitter, who said: "He wants four more years of Obama-but nobody else does!"

The response to him from Clinton's campaign was: "Delete your account."

However, Sanders, who has a fan following among young voters with his rousing call for greater social equality and efforts to rein in Wall Street is not willing to back out, even as Democrats seem keen to support Clinton's bid to beat Trump.

Obama and other senior Democrats are thus walking the tightrope of getting the party behind Clinton, without alienating Sanders and his supporters.

Obama invited and spoke to the Democratic socialist Sanders for an hour in the White House.

However, Sanders told reporters that he will still compete in the final nominating contest in Washington, D.C. on June 14. But he wanted to work with Clinton to defeat Trump.

On Capitol Hill, he was welcomed by Senator Harry Reid, the top Democrat in the Senate. Reid said that Sanders was close to acknowledging defeat by Clinton.

"I didn't hear a single word about him trying to change the fact that she is the nominee, I think he's accepted that," Reid told reporters.