In politics, this day and time, there is no civility from either party. One of the biggest criticisms of Trump is his caustic tweets and responses toward opponents or anyone that speaks negatively of him. I, freely, admit that Donald Trump has one of the largest egos of anyone that I have ever seen but much of his braggadocio comes from who and what he was before entering politics. Trump is not a politician, certainly not a typical one, but is a businessman and from that background a ruthless businessman and that follows him in politics.
The fact that he is not a typical, sample the political winds, politician is one thing that is attractive to many voters and even though some of his behavior is somewhat objectionable he not only responds to attacks but he responds in the most overtly overwhelming manner. Not equal response but overwhelming domination and Trump is one who is certainly attacked frequently and often in unwarranted ways. Joe Biden is the current leading contender and although I honestly believe Warren or Harris will be the Democrat candidate Trump will face I can understand the jabs at Biden for fulfilling the gaff predictability.
Look at it this way, if you are a Democrat I would think you would want unmercifuil attacks and trials against all potential candidates because if you wait for the actual candidate to be selected without each passing through the fire of political torment and political combat then you could possibly end up with a candidate that is not as capable of standing up against the torrent of abuse that will surely come from the Republicans, Trump and Trump supporters. Better find out now which candidates are weak than wait for the actual 2020 campaign to begin.