My rough guess is that about 40% of them might be persuaded to vote, overwhelmingly the men. George W. Bush's campaign made significant effort in 2004 and got maybe half that number.
At the time, most of them offered to pray for him but weren't much interested in registering to vote. Things may have changed a lot in 12 years.
Most Amish understand that they need to make minor compromises to live in modern era. They can use power tools as long as someone else owns them. They can even have phones as long as it is a community type phone in a booth outside their homes. That includes mobile as well as landlines.
They still have large families and the custom of sending their kids out to live among the English (non-Amish) for two years as they reach adulthood. Those who decide not to return face considerably less shunning (ostracism) as in the past. On the contrary, many become valuable contacts to promote more business opportunities with the non-Amish world. This includes a lot, lot more than building barns and selling agricultural produce now.
Indiana comes in third according to my reading. The oldest community was founded around 1841.