There are many, very many reasons to vote against your Republican Party in the midterm elections, the most important of which is to reinstate the checks and balances only the Legislative Branch can provide.
1.- For the past eight years, Republican Party has been in control of both Houses (Congress & the Senate) and they have made it a norm to let scandals and corruptions in the Trump administration go unchallenged, uninvestigated
2.- For two years now, the United States is run like a banana Republic. Despite the many scandals which have plagued the Trump’s administration and the rampant corruptions in Washington, there is not a single Congressional investigation to seriously look into those matters. Republican Legislators and the White House have proven – with no room for ambiguity – that you the constituents do not matter