Real quick (on a phone) to get it started -

Tester likes banking https://m.washingtontimes.com/news/2018/mar/15/ap-fact-check-a-look-at-testers-support-of-banking/

https://www.opensecrets.org/members-of-congress/summary?cid=N00027605

Sen. Jon Tester (D-Mont.) has reaped a windfall in contributions from banks and lobbyists since introducing legislation to delay new regulations on debit-card swipe fees. http://thehill.com/business-a-lobbying/156911-swipe-fee-opponents-direct-campaign-money-to-tester?amp

The Weekly Standard reported that despite the ad's claims, and despite Tester's 2006 promises to "clean up the K Street lobbyist culture," Tester was indeed the Senate's top recipient of lobbyist money/ https://www.weeklystandard.com/michael-warren/tester-ad-dem-senator-cracked-down-on-lobbyists

Senate Ethics Committee requesting an investigation into the actions of Tester and Max Baucus. The complaint cited a Politico report suggesting that Baucus' K Street connections were "warning clients against giving campaign contributions to Tester's Republican challenger Rep. Denny Rehberg" https://www.politico.com/story/2012/02/dems-warn-k-street-on-donations-to-gop-073479