To me, I would make the electors in each State go by their congressional districts, with the 2 electors for senator determined by State-wide vote.
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Dividing more states’ electoral votes by congressional district winners would magnify the worst features of the Electoral College system.
If the district approach were used nationally, it would be less fair and less accurately reflect the will of the people than the current system. In 2004, Bush won 50.7% of the popular vote, but 59% of the districts. Although Bush lost the national popular vote in 2000, he won 55% of the country's congressional districts. In 2012, the Democratic candidate would have needed to win the national popular vote by more than 7 percentage points in order to win the barest majority of congressional districts. In 2014, Democrats would have needed to win the national popular vote by a margin of about nine percentage points in order to win a majority of districts.
In 2012, for instance, when Obama garnered nearly a half million more votes in Michigan than Romney, Romney won nine of the state’s 14 congressional districts.
Nationwide, there are now only 10 "battleground" districts that are expected to be competitive in the 2016 presidential election. With the present deplorable 48 state-level winner-take-all system, 38+ states (including California and Texas) are ignored in presidential elections; however, 98% of the nation's congressional districts would be ignored if a district-level winner-take-all system were used nationally
The district approach would not provide incentive for presidential candidates to poll, visit, advertise, and organize in a particular state or focus the candidates' attention to issues of concern to the state.
In Maine, where they award electoral votes by congressional district, the closely divided 2nd congressional district received campaign events in 2008 (whereas Maine's 1st reliably Democratic district was ignored).
In 2012, the whole state was ignored.
77% of Maine voters support a national popular vote for President
In 2008, the Maine Senate passed the National Popular Vote bill
In Nebraska, which also uses the district method, the 2008 presidential campaigns did not pay the slightest attention to the people of Nebraska's reliably Republican 1st and 3rd congressional districts because it was a foregone conclusion that McCain would win the most popular votes in both of those districts. The issues relevant to voters of the 2nd district (the Omaha area) mattered, while the (very different) issues relevant to the remaining (mostly rural) 2/3rds of the state were irrelevant.
In 2012, the whole state was ignored.
74% of Nebraska voters support a national popular vote for President
After Obama won 1 congressional district in Nebraska in 2008, the only state in the past century that has split its electoral votes between presidential candidates from two different parties, Nebraska Republicans moved that district to make it more Republican to avoid another GOP loss there, and the leadership committee of the Nebraska Republican Party promptly adopted a resolution requiring all GOP elected officials to favor overturning their district method for awarding electoral votes or lose the party’s support.
A GOP push to return Nebraska to a winner-take-all system of awarding its electoral college votes for president only barely failed in March 2015 and April 2016.
Awarding electoral votes by congressional district could result in no candidate winning the needed majority of electoral votes. That would throw the process into Congress to decide the election, regardless of the popular vote in any district or state or throughout the country.
Because there are generally more close votes on district levels than states as whole, district elections increase the opportunity for error. The larger the voting base, the less opportunity there is for an especially close vote.
Also, a second-place candidate could still win the White House without winning the national popular vote.
A national popular vote is the way to make every person's vote equal and matter to their candidate because it guarantees that the candidate who gets the most votes in all 50 states and DC becomes President.