Former vice-president Joe Biden announced his bid for the 2020 Democratic presidential nomination Thursday. The 76-year-old centrist Democrat faces a crowded field, which includes the progressive Senators Bernie Sanders and Elizabeth Warren.

Biden was the vice president of the United States from 2009 to 2017 and had decided not to challenge Hillary Clinton for the Democratic nomination in 2016. He had made two failed bids earlier for the White House, in 1988 and 2008.

Biden enjoys a good relationship with those across the aisle, but in the new political enviornment that could become a problem. Earlier this year he had described Vice President Mike Pence a "decent guy" at a speech in Nebraska but had to walk back that comment after it drew furor from the left, which cited Pence's stand on LGBTQ rights.

He is also known as a "touchy feely" politician and recently two women had complained about it -- one was Lucy Flores who said he kissed her on the back of the head at a campaign event when she was running for lieutenant governor; and the other Amy Lappos, a former aid to a congressman, who said Biden touched her face and both hands and rubbed noses with her.

For sure many women have come to his defense, saying they never thought his physical contact was inappropriate. But in a crowded field in a party that is being pulled to the left, all that will come under fresh scrutiny.

In his campaign annoucement video, Biden took aim at Trump, for the latter's comment in the aftermath of the white supremacist rally in Charlottesville, Virginia, in August 2017, saying the president "assigned a moral equivalence between those spreading hate and those with the courage to stand against it."

And Trump, who employed taunts and mockery to great effect in the 2016 race, hit back through a tweet in his trademark style soon after: "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! "

If anything, Trump's tweet is a sign of what awaits Biden if he snags the Democratic nomination: Trump made short work of the challenge from Jeb Bush for the Republican nomination in 2016 with comments of a similar nature, repeatedly calling him "low energy Bush."