Why did the popular election of presidents mean that campaigns now had to be conducted on a national scale?

All voters should be valued equally in presidential elections, no matter where they live. Our current Electoral College system, grounded in state laws which allocate electoral votes on a winner-take-all basis, leads presidential candidates to concentrate their resources on voters in a handful of swing states, relegating the vast majority of the country to spectator status. Instead, we should elect the president by a national popular vote—and there's a state-based, constitutional way to do so: The National Popular Vote interstate compact.

Explanation:

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one of the negative side effects were the economic losses the events of september 11th caused. many, many people lost their jobs as a result of a downturn in the economy after the terrorist attacks.

offline recommendation systems option b

because recommendation systems produce a list of two ways

1. through collaborative filtering

or

2. through content-based filtering