We'll just assume that you have been asleep these past four years.
The DNC will decide. Of course, if the DNC has decided that Biden is out, they will ask nicely at first, and will gradually ramp up the pressure until Biden is simply no longer the DNC's candidate, if that is what it has to come down to.
Otherwise, if the DNC has decided that Biden is in, because the DNC is confident that it can steal this election as well, then all of this public "pressure" for Biden to step down is merely a side show that the DNC permits so that they can portray Biden as staunchly displaying his fiery independence and his raging resolve to claim the Presidency. Of course, this imagery won't jibe with Biden's meek babbling and his need to be told to stop talking to his imaginary friends, but at such a point in time, Biden's handlers won't give a shit about any of that.
We have to follow the law, and that is what is spelled out in the Constitution.
Trump cannot lose if it is a free and fair election. That last part is what is in question.
That will be how any rational adult will be able to tell if the DNC was successful in stealing the election.
Don't worry; I have you listed as one of the seventeen people who are going to be actually be voting for Biden. I was, of course, exaggerating when I said that nobody was going to be voting for Biden.
The Constitution outlaws nobility, and Trump is running for the Presidency which is spelled out in Article 2.