Congress is actually getting less partisan, and has been for a few years. That's the somewhat surprising conclusion of an analysis done using data on co-sponsorship of legislation done by Quorum, a company that specializes in quantitative information about American politics.
The variable tracked here is what share of bills introduced have at least one co-sponsor from the other party. And we can see here that while bipartisan bill writing is still well below its historical average levels, it has bounced back — especially in the Senate — from the nadir it reached in the 112th Congress.
It's interesting to note that the small-scale revival of bipartisanship has happened even though we haven't seen any kind of meaningful resurgence of ideological moderates on Capitol Hill. The broad structural forces (the increasing clout of ideologically motivated donors, the disappearance of the white conservative Southern Democrat) pushing ideological sorting and polarization are still in effect, members are just learning how to write a bipartisan bill or two even in a polarized climate, most likely by focusing on less significant issues that are less central to the main conflicts in American politics.