Why does partisanship typically become a major obstacle in the impeachment process?

The impeachment process is prescribed in the Constitution. However, history has shown that partisan opposition from Congress is key to trial an impeachable offense.

James Buchanan, Ulysses S Grant, Harry Truman, and Ronald Reagan had sufficient backing in Congress to suffocate any attempts towards impeachment hearings even when there was evidence that there might be a reason to do so.

in the 1800s, locomotives powered by steam made transportation faster and cheaper. the resulting rapid growth of railroads led to the connection of the atlantic and pacific railroad in oklahoma city in 1897.

in the last years of the century, the improvement of steam-based engines the expansion and growth of railroads. this growth increased when the companies started to build and expand, such as the atlantic and pacific railroad, which connected new mexico with california, and missouri with oklahoma. many of these new networks were built in oklahoma, and these changes transportation henceforward.

after defeating german forces in north africa allied leaders turned their attention to "italy," since this was the location that made the most geographic sense before invading northern europe via france.