Executive Summary: PA certifies on Nov. 23rd, which should end any doubt. SCOTUS appeals follow, which should fail. Trump is left only with a nuclear option at that point.... which, while unlikely, does leave him a path to the Presidency.
Have you asked yourself, "What do they think they are doing?!" If there is any path open to the presidency, you can expect that he will pursue it to the end. While I do not believe that any of these paths will be productive, I do expect that he will go down these roads in any event.
1) Local lawsuits to overturn votes in his favor prior to state certification;
2) SCOTUS appeals to overturn results, after certification;
3) Appeals directly to Republican State Legislatures to appoint electors contrary to their state's certification, after losing before SCOTUS.
All 3 of those options would need to be concluded prior to Dec 8, as the electors must submit their votes by Dec 9.
State Certification Dates
As of Nov. 10, the Trump administration's GSA office is refusing to sign a statement of Ascertainment. The formal statement recognizes the apparent results of an election and allows the peaceful transfer of power to have a leisurely period of preparation. There is no legal mandate for the GSA to ascertain, and in Gore/Bush it did not do so until after the final ruling of the SCOTUS.
Key to the GSA's legitimate delay are the individual certification dates of the many states. Prior to a state's certification of its own results, and the resultant naming of electors, the GSA can theoretically determine that there is not an absolutely clear victor. Once certification occurs, it is nearly impossible to overturn it or ignore it.
Here are all the states' certification dates, but I include here for you the most contested states. These are their real deadlines. Again, as in the main election, Biden needs 3 or 4 of these to win.
State Winner Date Who Certifies (Party)
Georgia Biden 11/20/2020 Sec. of State (R)
Michigan Biden 11/23/2020 State Board of Canvassers (split)
Pennsylvania Biden 11/23/2020 Secretary of the Commonwealth (D)
North Carolina Trump 11/24/2020 State Board of Elections (D)
Arizona Biden 11/30/2020 Sec. of State (D)
Nevada Biden 12/01/2020 NV supreme ct & Sec of State (R)
Wisconsin Biden 12/01/2020 Chair of Elections Commission (split)
Just for fun, assuming that all of the current outcomes hold up, here is the actual timeline of certification and the Electoral College vote tallies to win 270. Sadly, the deadlines lead all the way up to the Constitutional deadline. Basically, whenever CA certifies, Biden will be the certified President-Elect.
These would have to be done prior to Dec. 8, if they hope to have a last minute victory in the Supreme Court, as all electors must vote in the Electoral college by December 9, 2020 after which there is nothing anyone can do, even the SCOTUS. SCOTUS was very concerned in 2000 that the State certification be respected. Barring widespread systemic manipulation, it is hard to see them overturning any certified result.