Since the movement launched in 2006, National Popular Vote has made significant progress to reform the way Americans elect their president.

The group's plan involves a state-by-state approach. States that join the National Popular Voter Interstate Compact (NPVIC) agree that rather than having their electors cast their ballots for president according to whichever candidate won the most votes in their respective states, the electors will instead vote for the candidate who won the most votes nationally.

The reform has been endorsed by past and present presidential candidates.

In 2014, former Republican presidential candidate Newt Gingrich expressed his support for the measure in a letter to Dr. Koza, the chairman of National Popular Vote. Expressing his disapproval of how the Electoral College affects presidential campaigning, Gingrich wrote:

The winner-take-all method of allotting electoral votes means candidates must focus their efforts on just a handful of closely divided states – Ohio, Florida, and Virginia being current examples. In fact, only 12 states received any attention at all from the nominees of either party in the most recent general election campaign.

Former Green Party presidential candidate Ralph Nader made a similar point in a recent article in Dissident Voice. Nader explained that when running for president, he visited all 50 states. He called it "disrespectful to the American people" that most candidates limit their campaigning to the states most critical to patching together the 270 electoral votes needed to win the White House.

At least one current presidential candidate competing in the 2016 election has supported this reform. Democratic candidate Martin O'Malley became the first governor to sign the bill into law after the Maryland General Assembly approved the measure in 2007.

Since then, 9 other states and the District of Columbia have joined the NPVIC. When New York became the last to join in April 2014, it brought the total number of electoral votes among its members up to 165 – 61 percent of the total needed to decide the presidency.

The states' electors will only cast their vote for the popularly chosen candidate once the number of electors from member states meets or exceeds 270.

While some argue that the reform movement is a ploy to circumvent or abolish the Electoral College and is thus a violation of the Constitution, supporters point to Article II, Section 1 of the Constitution, which says, "Each state shall appoint, in such manner as the Legislature thereof may direct, a number of electors, equal to the whole number of Senators and Representatives to which the State may be entitled in the Congress."

In other words, the Constitution dictates how many electors vote on behalf of each state, but not how they ought to vote – a decision left to state legislatures.

Supporters cite numerous upsides of switching to the national popular vote model.

First, it ensures that each vote counts. For example, it would have meant that the 4.8 million votes for Romney in California and the 3.3 million votes for Obama in Texas would not have been for naught.

Second, and relatedly, it would increase voter turnout. Under the current rules, those in battleground states are more likely to vote because their votes are much more influential: in 2012, the voter turnout rate was 8.8 percent higher in more competitive states compared to less competitive states. Under the proposed system, however, the national turnout rate could shoot up well above the standard 60 percent figure – possibly with unforeseen consequences.

Third, it would incentivize candidates to visit each state and not result in the disproportionate attention to "swing states," as cited by Newt Gingrich. In 2012, two-thirds of all general election campaign events were held in four states: Ohio, Virginia, Florida, and Iowa. By making each vote count in each state, it would force candidates, in the words of Gingrich, "to run truly national campaigns, addressing the concerns of Americans in all 50 states."

Finally, the reform could prevent the politically-motivated allocation of government resources. According to a report by Reuters, between elections, swing states receive preferential treatment from the federal government in discretionary grants. For example, between fiscal years 2009 and 2012, Ohio saw a 21 percent increase in the number of grants it received, whereas the number of grants to reliably "red" Texas dropped by 37 percent over that same period.

Reuters concluded that the executive can allocate spending as a kind of "publicity tool for a president looking to show voters how he's making a difference in their communities." Under the proposed system, however, the concept of the swing state would evaporate, and along with it, the politically-motivated distribution of discretionary funds to electorally crucial states.

Critics see the reform as distinctly partisan. All 10 states that have joined the NPVIC (Maryland, New Jersey, Illinois, Hawaii, Washington, Massachusetts, Vermont, California, Rhode Island, and New York) and the District of Columbia voted for President Obama in 2012. Also, except for the 2004 election, Democratic presidential candidates have won the popular vote since 1992 – including the 2000 Bush vs. Gore election, when Gore lost in the Electoral College despite winning the popular vote by 540,000 votes.

However, political strategists show that the reform may negate the Democrats' projected advantage in the Electoral College: most configurations of the map appears to benefit the Democratic nominee in 2016. Analysts Larry Sabato, Kyle Kondik, and Geoffrey Skelley observe, "For the Democrats, a victory in 2016 entails zero expansion of the blue map, merely the limiting of blue-to-red transformations. Republicans, they note, "must hold all their usual states plus find a way to stitch together an additional 64 electoral votes, or 79 if they can’t hold North Carolina."

For the national popular vote plan to go into effect before 2016, it would require states with a combined 105 electors to join the NPVIC.

In February, Oklahoma decided to review the idea next year. In May, Oregon took one step closer to joining the compact when the House approved the measure. The bill will move to the Senate, where the proposal has been defeated in the last three sessions.