Parties adjust. I remember after the Goldwater debacle in 1964, everyone was saying the Republican Party was dead. It would be at least 20 years, if not more before they became competitive in elections. I think the pundits and those saying that remembered Hoover and FDR being elected for four terms with Truman making it five in a row in 1948.
That was a bad election, LBJ won 61-39, The democrats had a 295-140 advantage in the house and a 68-32 advantage in the senate. But come 1968, Nixon won the presidency, The GOP had picked up 40 house seats and 10 senate seats.
Then came Watergate, Carter elected president in 1976, he was given 292-143 advantage in the House and a 62-38 advantage in the senate. Again, everyone was saying it would be 20-30 years before the GOP won an election.
Then came 1980, Reagan won, 49 house seats switched and the Republicans won the senate. Now everyone was talking about the Republican lock on the presidency. Several books were written about that. But in comes Bill Clinton in 1992. So I heard all of this before and seen the results.
I think you're missing something here. In 2006 only 30% of the electorate were independents with the Democrats having a 37-33 advantage over the Republicans. Today, 40% of the electorate have become independents as the two parties have shrunk. Gallup as of 22 Mar 2020, list both those who affiliate or identify with Republicans and Democratic Parties at 30% each.
As the two parties move further and further left and right, more moderates are leaving both parties. The Democratic Party averaged between 45-50% of the electorate from the end of WWII until Reagan, then 35% until Obama and now are at 30%. The GOP average around 25% of the electorate since Eisenhower through today. The high for the Democratic Party was 51% in both 1961 and 1964, Their low is 30% as of 22 Mar 2020. The GOP had their high of 38% in 1942, their low of 21% in 1975, but have slowly climbed back to 30% as of 22 Mar 2020.
It's high past time that we start electing Americans to congress and the presidency who put America first instead of their political party. For way too long we have been electing Republicans and Democrats who happen to be Americans instead of Americans who happen to be Republicans and Democrats.