Ohio has been trending right because aside from Greater Columbus and rural areas the state has been hemorrhaging voters. The population growth in Columbus is in largely the result of people leaving some strong-D urban areas who do not go to other states. Columbus keeps Ohio from becoming another Missouri, but it is not attracting people from outside Ohio.
The trend is OH is becoming another MS, just not yet.
lol
Anyway, what everyone else has said is mostly right. But also: a very aggressive gerrymander broke Democrats' ability to recruit anyone to anything above Mayor outside the major metro areas and Athens, which has had a debilitating effect on candidate recruitment. Columbus becoming the juggernaut for Ohio Democrats has been damning, as people from across the state resent it terribly.
Pack and sack. The typical gerrymander works by conceding that a big city has areas that might be 70% D, so the Republicans concede as much of that as is necessary that much of the rest of the state can be sliced like pizza except that small areas that are about 70% D are overwhelmed by rural areas that are 60% R. This way the state legislature can be designed for a permanent 3-2 split, and the minority party must bow and scrape to get anything. The opposition becomes impotent, ineffective, and irrelevant. That's not quite Iraq under Saddam Hussein or North Korea under the Kim dynasty, but that also works well for a permanent and unassailable majority.
The old German Democratic Republic (East Germany) was technically a multi-party system, but the Communists could ensure that the Communist-dominated coalition had a large-enough majority that it could ram through practically any legislation that it wanted with little discussion. That could well serve a right0wing, crony-capitalist party, too.
