Twice in the past five presidential elections, a Republican has won the presidency despite losing the popular vote. Now Democratic Sen. Brian Schatz of Hawaii has introduced a constitutional amendment to abolish the Electoral College and use the national popular vote to decide who becomes president. His proposal is among the latest efforts by Democrats and those on the left to push for structural changes to the American political system.

But Schatz’s amendment is sure to meet defeat in the Republican-controlled Senate. Today, attitudes toward the Electoral College are polarized by party, with Democrats far more likely to support a change and Republicans much more likely to defend the current system — but it wasn’t always like that.

While the controversial 2000 election was still being decided, Gallup found that 61 percent of Americans — including 73 percent of Democrats and 46 percent of Republicans — preferred amending the Constitution to elect the popular vote winner. Only 35 percent of respondents preferred the current system. The partisan gap widened even further after the 2016 election: A few weeks after President Trump won the presidency while losing the popular vote, Gallup found that 49 percent of Americans preferred changing to a popular vote system, compared to 47 percent who wanted to keep the Electoral College, with 81 percent of Democrats supporting a change compared to just 19 percent of Republicans. Even given some space after that heated election, there remains a major partisan gap in opinion over how to elect a president — Pew Research found in March 2018 that 75 percent of Democrats supported moving to a popular-vote system versus only 32 percent of Republicans.

But 50 years ago, moving on from the Electoral College had bipartisan support. In May 1968, 66 percent of American approved of the idea of amending the constitution to replace the Electoral College with a popular vote system, according to Gallup. And there was no partisan divide: 66 percent of Republicans and 64 percent of Democrats approved. Six months later, Republican Richard Nixon defeated Democrat Hubert Humphrey while only winning the popular vote by less than 1 percentage point, and a post-election Gallup survey found 80 percent of Americans approved of changing the electoral system. The bipartisan support among voters and the fact that the 1968 election nearly produced a split between the popular vote and the Electoral College explain why there was bipartisan support in Congress in 1969 for a constitutional amendment to elect presidents based on the popular vote. The House passed it 339 to 70, with more than 80 percent of each party’s voting members lending their support. But small-state senators from both parties filibustered the amendment and it never got an up-or-down vote in the upper chamber.

As long as one side feels disadvantaged by the Electoral College, it will be far more likely to push for a popular-vote system. Right now, that’s the Democrats. Reforming how the country elects presidents falls into the broad effort on the left to reform aspects of our electoral system, including voting access and how campaign finance works. But some who want reform believe abolishing the Electoral College should be a secondary goal. “There’s a bunch of stuff to do without amending the constitution that would have the end result of making institutions and elections more fair,” said David Faris, a political scientist at Roosevelt University, who recently argued in his book “It’s Time To Fight Dirty” that Democrats should be challenging the structural and legal boundaries of the American political system to better gain and hold power. Nonetheless, Faris sees discussion over the electoral system as a good thing in that it could soften up public opinion and make people more willing to consider alternatives to the status quo.

But we may not see a true shift in public opinion unless a Republican loses in the Electoral College while winning the popular vote. As FiveThirtyEight has argued in the past, the system is not inherently biased against either party, with one side’s seeming advantage lasting for just an election or two before it flips to the other party. But as the 1969-1970 example shows, it seems likely that only serious bipartisan support for abolishing the Electoral College system could ever change how we elect a president. Although states may figure out a way around the Electoral College with the National Popular Vote interstate compact, it would not seem as permanent as a constitutional amendment, given that only one amendment has ever been repealed. And as Faris argues, using the interstate compact method might precipitate a crisis because an outcome might be seen as illegitimate and be subject to legal challenges if it delivers a result that contravenes what the Electoral College would otherwise do.

Schatz’s proposal is unlikely to pass the Senate, but it may be a symbolic effort to influence the conversation about what we want our electoral system to look like. Nonetheless, without broader agreement, a constitutional amendment to abolish the Electoral College will pass when pigs fly.

Sen. Elizabeth Warren wants to get rid of the Electoral College