There are many conspiracy theories being discussed on many social platforms and it is not surprising that many Trump supporters suspect the Democratic Party of being the mastermind behind this assassination. But I don't think the Democratic Party or Biden are behind this because this will have huge consequences for American politics and if it fails, it will cause huge damage to the Democratic Party.
There have not been any announcements or disclosures related to Mr. Trump's assassination, but according to many news, the person who shot Mr. Trump was also a Republican but had donated to Biden.
All of this shows that US politics is too unstable and degenerate.
https://www.dailymail.co.uk/news/article-13632783/donald-trump-gunman-revealed-registered-republican.htmlConspiracy theories are going to be launched in an attempt to discredit the legitimacy of the attack, trying to drive public opinion to believe it was forged by Trump in collusion with his team to generate social commotion. It's part of the political strategy at this moment.
The fact the gunman is registered as a republican being heavily shared as an alibi for the Democrats, already display this strategy, while the most logical alternative is that the man disguised himself as a republican to have access to republican's events, so he could execute his plan.
Even if Democratic party isn't the mastermind behind the assassination attempt, the brainwashing they execute saying Trump is fascist, racist, misogynistic and every other labels they like gluing on others to leverage their own political interests, is indirectly responsible for the concept the most vulnerable individuals elaborate regards Trump.
Trump is just a politician like any other, with his own personal interests, agenda and greed for power. What differs one side from another are the methods used in the present time, although both are still sides of the same coin.