Or they may just realize they can't possibly get a conviction even with legitimate scandals so it will backfire like the Clinton one did.
Spec is right, if they had anything real they would have tried already. Right now all they have is stuff that won't survive outside the conservative bubble. All of their "scandals" have been exposed as bullshit and if they tried to impeach Obama with bullshit they would implode. If they had anything they would be pushing for impeachment.
If it were something real, like Watergate, then people would get behind them. Anything short of that will backfire.