Another problem occurs in every presidential election, namely that presidential candidates have no reason to campaign in, or pay attention to, voters in states where they are safely ahead or hopelessly behind.
In 2012, 100% of the general-election campaign events (and virtually all campaign expenditures) were concentrated in the 12 closely divided "battleground" states where Romney's support was 45%-51%. Thirty-eight states were totally ignored, including almost all small states, medium-sized states, rural states, western states, southern states, and northeastern states. Two-thirds of the events (176 of 253) were concentrated in just 4 states (OH, FL, VA, IA).
Similarly, in 2016, almost all (94%) general-election campaign events were in the 12 battleground states where Trump's support was in the narrow range of 43%-51%. Two-thirds of the campaign events (273 of 399) were in just 6 states (OH, FL, VA, NC, PA, MI).
It does not take an amendment to the U.S. Constitution to change existing state winner-take-all laws. State winner-take-all laws were enacted by state legislatures under their authority under Article II of the U.S. Constitution:
"Each State shall appoint, in such Manner as the Legislature thereof may direct, a Number of Electors...."
These state laws may be changed in the same way as they were originally enacted -- namely by action of the state legislature.
The winner-take-all method of awarding electoral votes was not the Founding Fathers' choice. It was used by only three states in the nation's first presidential election in 1789 (and repealed by all three by 1800). Winner-take-all was never debated at the Constitutional Convention or mentioned in the Federalist Papers.
The National Popular Vote interstate compact will go into effect when enacted by states with a majority of the presidential electors—that is, 270 of 538. After the compact comes into effect, each individual voter in all 50 states and DC will acquire a direct vote in the choice of all of the presidential electors from all of the states that enacted the compact. The presidential candidate supported by the most voters in all 50 states and DC will thereby win a majority of the presidential electors in the Electoral College (at least 270), and therefore become President.
The National Popular Vote bill is an achievable political goal. A record 4 states enacted the National Popular Vote bill in 2019. The bill is now law in 16 states. These states have 196 electoral votes. This is only 74 short of the 270 needed to activate the bill. The bill has been enacted into law by 5 small jurisdictions (Delaware, Hawaii, Rhode Island, Vermont, and the District of Columbia), 8 medium-sized states (Colorado, Connecticut, Maryland, Massachusetts, New Jersey, New Mexico, Oregon, Washington state), and 3 big states (California, Illinois, and New York). It has also passed one house in 8 additional states with 75 electoral votes (AR, AZ, ME, MI, MN, NC, NV, OK). A total of 3,408 state legislators among all 50 states have endorsed it.