Since Congressional districts are equal in population, if enough states do this, won't Gore win in 2000 and Clinton in 2016?
No, no, no, no, no. Even apart from deliberate gerrymandering (which is done by both parties, but the Republicans had far more opportunity to do it in the 2010's and even in the 2000's because of their control of more state legislatures) choosing electors by congressional districts would favor the Republicans simply because Democrats are far more concentrated in ultra-partisan congressional districts. E.g., in 2016, only one congressional district went over 80% for Trump--AL-04 with 80.4%. By contrast 24 congressional districts went over 80% for HRC! The concentration of Democratic votes in these (mostly heavily African American and Hispanic) districts hurts the Democrats in (relatively) closer districts. "Despite losing the national popular vote by 2.1 percent, Donald Trump carried 230 congressional districts and Hillary Clinton just 205..."
https://www.dailykos.com/stories/20...al-election-results-by-congressional-district
I'll quote an old post of mine:
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As I indicated earlier, 2012 would have changed; Romney won 226 congressional districts to Obama's 209.
http://cookpolitical.com/file/2013-04-50.pdf
2008 and 2000 would not have changed. In 2008, Obama carried 242 congressional districts, McCain 193.
http://blog.timesunion.com/rogergre...nebraska-rules-would-obama-still-have-won/380 In 2000 Bush won 228 congressional districts to 207 for Gore.
http://www.polidata.org/press/wpr1c20z.pdf (Given that Gore actually won the popular vote and came very close to winning the Electoral College in OTL, this relatively comfortable Bush victory in congressional districts shows that a congressional-district method is somewhat weighted toward the Republicans even when they do not have a gerrymandering advantage-- because Democrats are hurt by the "clustering" effect.)
1980 would definitely not have been changed. Reagan carried 308 congressional districts that year.
http://www.washingtonpost.com/pb/ar...4484-af99-ce8254ac348a/?resType=accessibility I think the reason you mistakenly thought 1980 would have been changed is that the Democrats won the majority of House seats that year. But in those days there was a big difference between how people voted for president and how they voted for Congress. Especially in the South and border states many people voted for a Republican presidential candidate but for (usually conservative) Democrats for Congress. In Oklahoma, for example, Reagan carried all six congressional districts in 1980, yet the state elected five Democratic congressmen to only one Republican!
Incidentally, the congressional-district method would have elected Nixon in 1960. He carried 228 congressional districts to 206 for JFK and three for unpledged electors.
https://library.cqpress.com/cqalmanac/document.php?id=cqal64-1302939 (There were temporarily 437 House seats because of the admission of Alaska and Hawaii to the Union.)
The most interesting result would have been 1976. Carter won 220 congressional districts to Ford's 215--but Ford carried 27 states to Carter's 23. Result: a 269-269 tie and the election goes into the House!
http://www.washingtonpost.com/archi...kennedy/f4a1ef3a-3df6-4dfd-aa3f-84932a88bd91/
There is just no getting around it: In any reasonably close election in recent decades, a congressional-districts apportionment (plus two votes at-large for the winner in the state) will favor the GOP in the Electoral College (though I think Carter would win in the House in 1976--the Democrats controlled more delegations). Once again, this is not due so much to the Republicans controlling redistricting (though they had an advantage in that respect after the 2010 election and even to a lesser extent after the 2000 one) as it is to the Democrats' "clustering" problem.
(Yes, I know it is unrealistic to assume that everyone would vote exactly as they did in OTL, but that doesn't change the basic point.)
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I might add a striking fact here. As you know, Doug Jones (D) narrowly defeated Roy Moore (R) in the Alabama special election for the US Senate. Nevertheless, Moore carried six of Alabama's seven congressional districts! He carried all the white-majority districts--much less overwhelmingly than Trump did, but he still carried them. Meanwhile, Jones only carried the predominantly African American 7th District. Yet his huge majority there, coupled with large minorities in the other districts, was enough for a narrow win. That shows you how far "who carried the most congressional districts" can be from "who won the popular vote"...
https://www.washingtonpost.com/news...t-still-won-the-state/?utm_term=.f4c61bf8dec0