All eleven states (plus D.C) that have so far joined the National Popular Vote Interstate Compact voted for Democrats in every presidential election since 1992.  Moreover, at the time of enactment, Democrats controlled the entire legislative process in eleven of the twelve jurisdictions. 

In 2000 and 2016, Republican candidates lost the popular vote but won the Electoral College, so it's understandable why many Republicans refuse to support the NPVIC:  They think the Electoral College system helps their party.

As long as that belief prevails, the Compact cannot reach the 270 electoral vote threshold it requires to go into effect.  At present, there are just seven more states where Democrats either control the legislative process (Delaware and Oregon) or could plausibly control it after the 2018 elections (Colorado, Maine, Minnesota, Nevada, and New Mexico).  These states--all small or middle-size--have just 45 electoral votes combined.  Even if NPV supporters ran the table, the Compact would still be 57 votes short of the goal. 

Thus, several states where Republicans control one or more branches of government must pass the NPVIC if it is to take effect in the foreseeable future.  Understanding this fact of life, NPVIC organizers worked with some success to win over Republicans.  Between 2014 and 2016, three chambers with Republican majorities voted in favor of the Compact--the New York and Oklahoma Senates and the Arizona House.  Unfortunately, the Electoral College 'inversion' that made Donald Trump President put a stop to such progress, because it renewed the belief in a Republican Electoral College advantage.

Obviously, the Electoral College did help Republicans in 2000 and 2016.  But is it true that the College regularly and systematically tilts the playing field toward Republican candidates?  To answer that question for elections with no actual inversion, analysts ask: which party could have won a 'wrong-winner' election?

Consider 2004, when George W. Bush defeated John Kerry in the popular tally by more than 3 million votes and in the Electoral College by 286-251.  However, if just 59,301 voters in pivotal Ohio had switched from Bush to Kerry, the Democrat would have won the Electoral College (271-266) while still losing the popular vote by a wide margin. 

Cherry-picking results in this way--swinging just enough votes in the minimum number of crucial states (only one in 2004)--makes it too easy to find potential inversions.  Instead, political scientists prefer a tougher test:  Would an inversion occur if the percentage swing required to flip the pivotal state happened in all states?  By this stricter method, called a uniform swing analysis, Kerry could still have won a 'wrong-winner' election.  To change the outcome in Ohio required a swing of 1.06% (or .53% of voters switching from Bush to Kerry).  If the same swing happened in every jurisdiction, four more states would have flipped from Bush to Kerry, giving the Democrat a solid 297-240 victory in the Electoral College; but Bush would have continued to hold a majority of the popular vote (50.20% to Kerry's 49.79%).

Political scientists (and also Nate Silver, the well-known polling analyst) have applied the uniform-swing method to previous presidential elections.  Since 1972, when the current party alignment was well underway), they find the following breakdown of partisan advantage in the Electoral College:

•       Republican advantage:  1976, 1984, 1988, 1992, 2000, 2016

•       Democratic advantage:  1972, 1980, 1996, 2004, 2008, 2012

Over the past twelve elections, the underlying 'bias' of the Electoral College has been to Democrats just as often as to Republicans!  Moreover, history gives no reason to expect even a short-term advantage for one party or the other.  From one election to the next, the Electoral College advantage has been more likely to shift (seven times) than to stay the same (five times).

Thus it is an error for Republicans to infer from 2000 and 2016 that they benefit from an enduring advantage built into the Electoral College system.  Once they liberate themselves from that mistaken belief, Republicans will be free to put the national interest first by joining the movement to enact the National Popular Vote Interstate Compact.

Jack Nagel is Professor Emeritus of Political Science at the University of Pennsylvania.