Iowa is one of the largest corn producing states, and also the first to hold primary elections (technically it's a caucus, but still it's considered an important milestone). If you want to be president, you'd be foolish to be on the record going against corn subsides.
Huh? Every president could have done that in his second term.
Today Presidents don't make the law. Potential candidates (and their parties) do.
There's a great episode of The West Wing about the Iowa caucuses and the ethanol mandate.
Ag programs are byzantine and corn is subsidized several ways-- through price floors, crop insurance, the ethanol mandate, and import tariffs on sugar (which created the market for high fructose corn syrup, which is derived from corn). The model has failed in important ways and isn't directly transferrable to fruits and veggies. The biggest thing is that the value of the subsidies is capitalized into land prices-- there actually isn't a subsidy for corn at all, if you are new farmer, because you have to pay for it when you buy or lease land.
Yes, I encourage you to write to your reps about it.
The midwest senate seats are powerful and much easier to influence.