If you could change three things in the US constitution...

[politicus]

If you got to change 3 things in the US constitution, what would you chose?

My bid:

1. Have the House of Representatives elected for four years at the same time as the President.

2. Use proportional representation to elect the House.

3. Elect the President directly using a run-off between the two candidates with the most votes if none of the candidates got 50% in the first round.

[politicus]

What's with all the desire for PR for the House?  The size of the House would need to be considerably increased, well beyond a thousand, to have it work while keeping apportionment by States, and apportionment of the House by States is a minimal necessity for keeping our government a Federal one. For a country as large and diverse as ours is, a Federal system is a necessity, not merely a nicety.

Why? The federal government could easily organize federal elections without affecting the power of the states in other areas.

[politicus]

A Federal system needs its elected members to have ties to its local constituents, otherwise its constituent states have practically no way to impact Federal policy. 

You already have the Senate for that + the vast majority of congressmen would still be elected by constituencies placed within one state.

As a compromise you could do FPTP in the smallest states, it wouldn't affect the overall result of elections that much.