Former U.S. vice president Joe Biden announced Thursday he is seeking the 2020 Democratic presidential nomination, instantly catapulting him to the top of an increasingly crowded Democratic field vying to challenge Republican President Donald Trump.

The veteran Delaware senator and two-term vice president in the Obama administration has rivaled Sen. Bernie Sanders of Vermont and other Democratic presidential aspirants in recent polls, although it is uncertain whether he will be able to match their fundraising prowess. His experience in the areas of foreign affairs, criminal justice and domestic policy is unmatched by other presidential candidates.

In a message released on video, Biden said the core values of the United States and its standing in the world are at stake.

“I believe history will look back on four years of this president and all he embraces as an abhorrent moment in time,” he said. “But if we give Donald Trump eight years in the White House we will forever and fundamentally alter the character of this nation, who we are. And I cannot stand by and watch that happen.”

Trump responded on Twitter, saying, “Welcome to the race Sleepy Joe. I only hope you have the intelligence, long in doubt, to wage a successful primary campaign. It will be nasty – you will be dealing with people who truly have some very sick & demented ideas. But if you make it, I will see you at the Starting Gate!”

Recently, at least seven women, including a one-time candidate for lieutenant governor in Nevada, accused the 76-year-old politician of inappropriate touching, hugs and kissing at public events. While Biden has defended his past behavior as consistent with his lifelong effort to make a “human connection” with women and men alike, he pledged in a recent video to be “mindful” of people’s boundaries going forward.

Biden, who was born in Scranton, Pennsylvania, and later moved to Delaware, has been in national politics almost his entire career. After Biden won his first Senate race in 1972, he spent the next 36 years in the chamber. He then served as president Barack Obama’s vice president for eight years.

Shortly after Biden’s announcement, two current Democratic senators, Chris Coons of Delaware and Bob Casey of Pennsylvania, endorsed his candidacy.

Biden has twice before run for president, seeking the nomination in 1988 and 2008, but failed to gain much support from voters either time.

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