Delay would be
unconstitutional, UNLESS congress passed, and President Trump signed, a bill changing the date that states must certify their results/electors for the electoral college. That date takes place in December of 2020.
In effect, President Trump would have to, in all likelihood, remove HIMSELF from office by agreeing to sign such a law. Either that, or enough Republicans in congress would have to decide to throw the Presidency to Biden by overriding a Presidential veto.
The way the selection process for the Presidency (and Vice Presidency) works is that if no one gets the required number of electoral votes, then the House and Senate will select the President and Vice President, respectively, from among the top 2 vote getters for each office.
It is important to know that the house votes along STATE lines, so despite currently having more representatives, the Democrats make up the majority of house seats in a minority of the 50 states. The Senate simply votes as normal.
As currently constituted, the U.S. House and U.S. Senate votes for the President and Vice President would BOTH be controlled by the GOP.
Unless the Democrats have a killer performance and add enough house seats to their current ones, in key places to take the majority in a few more states, President Trump would have no incentive to sign, and Republicans in congress no incentive to pass, a law changing the date by which electoral votes must be certified, which again, is in December of this year. The new congress in January will merely TALLY those votes. They cannot alter that tally by allowing any state who refused to certify results by the deadline to add their electoral votes in. And the states most likely to have delay issues are the ones most likely to deny BIDEN 270 electoral votes - example
#1 would by California. In a scenario where Trump wins the election anyway, he probably does so even if there are states who cannot certify. None of the large red states like Texas are likely to have delay problems.