computer, eavesdropped on the Israeli Embassy's discussions with members of Congress in 2011, hacked the US Senate Intelligence Committee's computers for years, eavesdropped on the Israeli Ambassador in 2015 when he was in the same room meeting with US Congressmen and women about the Iran Deal (people often forget that one - Link below), and serially unmasked--with no justification whatsoever--the names of Americans innocently caught up in FISA warrants. Any Administration which acted this way would have no problem using opposition research to spy on the opposing campaign.
There is so much more to come, and I expect that the FBI's use of intelligence from FOREIGN governments (UK, Italy, and Australia) will be coming in to play soon.
Link: https://www.theguardian.com/world/2015/dec/30/us-spying-netanyahu-israel-iran-nuclear-deal-obama-nsa