What Frank ruined: Tusk's business interests
How he ruined it: By undermining Tusk's dealings with the Chinese
Why he ruined it: Because Tusk proved a worthy adversary to Frank

Throughout season two, Frank and Raymond were embroiled in a political and economic struggle revolving around trade with China. We'll skip all of the juicy plot points regarding currency manipulation. All you need to know is that there was some back and forth that ended with Tusk testifying against his longtime friend President Walker. This lead to Tusk's arrest and Walker's resignation.