The natural way to accomplish this is by a Constitutional Amendment, but that would be impossible to bring off, because there are enough small over-represented states in the nation to constitute a blocking one-third of the fifty states. This is not exactly an accident. The complicated political compromise that became our political system was originally designed explicitly to protect the institution of slavery -- the price the Southern states demanded for their participation in what today we call nation-building -- and to protect the smaller colonies from domination by the larger ones. As time has passed and our politics have evolved, the Electoral College system has served quite well to magnify the power and influence of the relatively small numbers of people who live in the lightly populated states.
Just to remind those of you who did not have the benefit of a Civics class in high school [mine was, as I recall, in my Freshman year, which is to say 1947], or who live abroad and find our curious political system too dense to penetrate, each state is assigned a number of Electors equal to the total number of its Members of the House of Representatives and Senate combined [hence a total of 535 in all]. The members of the House are allocated in a manner reasonably proportional to population, although the Constitution stipulates that each state must have at least one Representative, and there are actually several states so unpopulated that they do not even have 1/435th of the nation's population in their borders. But each state has the same number of Senators, and this rather dramatically unbalances the relationship between population and Electoral Votes.
The strategy behind the National Popular Vote Bill campaign is to recruit state legislatures to make a provisional commitment to allocate their Electors in a presidential race to whichever candidate gets the most votes nationally, the commitment to take effect once states having in total 270 Electoral votes have signed on. Once that happens, regardless of what the remaining states do, the states in the compact will be able to guarantee that the winner of the popular vote will get enough Electoral votes [i.e., 270] to win the election. For those with short memories, the last time the loser of the popular vote won the presidency was in 2000.
Because of the political complexion of the states with the most caches of Electoral votes, this effort is widely, and correctly, I think, seen as effectively an effort to push the country to the left, although of course nothing remotely like that is ever said by the proponents of the campaign.
Thus far, a dozen or more state legislatures have passed the bill [who knew?] representing about half of the 270 Electoral votes needed. If the campaign manages to persuade enough additional state legislatures to enact the bill [and assuming that the Electors vote in the Electoral College as their state legislatures have instructed them to do, something they are not required to do by the U. S. Constitution], presidential elections will henceforward de facto be contests for popular votes alone, without a word of the Constitution having been altered.
The effect on presidential campaigns would be electric. I think there is no doubt about that. As things are now, campaigns virtually ignore safe states, even those having huge caches of Electoral votes. No Democratic candidate is going to waste much time or money campaigning in New York or California, despite their size, because they are absolutely sure to vote Democratic, and a 55/45 victory yields exactly as many Electoral votes as a 60/40 or 65/35 victory. But if it is total votes, and only total votes, that count, then it makes very good sense to spend scarce resources getting one's supporters to the polls in safe states, because there are likely to be large concentrations of such additional votes in safe districts. If a ward or precinct regularly gives 85% of its votes to one party or the other, as happens in many places all over the country, the non-voters in that ward or precinct are likely to break in the same fashion. Why labor to locate and persuade a so-called "independent" voter in a swing state when with much less effort and money, you can get a reliable supporter to the polls?
As a political junkie on the left, I find this campaign intriguing. I can think of some powerful arguments against it, but I think I shan't mention them. hem hem.