The other GOP nominees to take one or more of those states in the last 120 years and yet lose the election:
Nixon took CA, VT and WA in 1964.
Dewey took NJ, VT, and MD in 1948.
Dewey took in VT 1944.
Willkie took VT in 1940.
Landon took VT in 1936.
Hoover took VT and DE in 1932.
Hughes took VT, DE, and IL in 1916.
Other than VT, it seems like this changes very little for any Republican candidate. It can only do great harm to a Democrat... up until undecided states or GOP-heavy states join, this is basically nonsense.
The problem today: Oklahoma and Nebraska both have bills in their Legislatures considering joining. If Oklahoma is in, THEN there's reason to worry about the Electoral College being destroyed. Until then, this can only lead to tiny losses of EVs for GOP candidates who stole a traditionally-Dem state... or massive EV losses for Dem candidates in the final, meaningless tallies, after the GOP candidate hits 270. Elections will go approximately 285-253 DEM, or else something like 428-110 for the GOP.
(Sorry... it’s RI, and not DE, in that list of current NPVIC members... mea culpa)