Most Partisan Modern President Besides The Obvious Two?

[Fuzzy Bear Loves Christian Missionaries]

FDR, all things considered.  Of course, FDR governed in an era where the GOP seemed a permanent minority. 

When I was a young activist in Democratic Politics, there were still oldtimers who remember FDR.  Lots of liberals who saw liberalism and the Democratic Party go through dark days after LBJ often thought things would have been different if FDR hadn't died.

[Fuzzy Bear Loves Christian Missionaries]

I would have thought Obama was one of the obvious two.

I do not really see the Nixon angle. Did not he pretty much let the Democratic Congress have free reign on domestic policy while he played geopolitical chess?

Nixson's resignation as a partisan is mainly from his VP days, and for his time in the wilderness running for Governor of California and campaigning for other Republicans.

As President, Nixon was primarily concerned with the ability to get majorities for his foreign policies.  He did not vigorously oppose those Democrats who supported his Vietnam War policy and foreign policies.  His Southern strategy did not seek to drive Southern Democrats from office in the Deep South; his goal was to neutralize George Wallace as a threat to him.