I have written a short piece for an online weekly, Kultura Liberalna, showing that, since the last Polish elections in 2015, the largest opposition party, the Civic Platform, has supported the PiS-led majority on almost 60% of all final passage votes. This evidence places a question mark over the claim that the PO provides an aggressive opposition to the PiS government. You can read the full article here (in Polish) and the raw data is available here.