Following the 2018 election and a long phase of negotiations, Lega and the Five Star Movement (FSM) appointed the first cabinet in Western Europe that does not include any mainstream party family. The "elective
affinities" between the electorates of these two challenger parties had been quite evident for some time, but in
the present work we argue that there are further traits that the two parties had shared well before 2018 that
could help proving even more their proximity. We propose a new dimension of analysis that should be taken into
consideration when studying (new) challenger parties: their relationship vis-\ue0-vis the other opposition parties. We
expect them to enter the parliament for the first time with both goals that are usually related to the two different
opposition status (temporary vs. permanent) in mind \u2013 leaving opposition and exploiting opposition \u2013, plus a
further one: standing apart from the other parties, no matter whether the latter are in government or in opposition.
That is, in fact, one of the main reasons of their electoral success and, in the end, their essence. We will test
these expectations by employing Social Network Analysis methods and analysing and comparing the cooperation attitudes of the Lega and FSM with the other opposition parties, using as an indicator the amount of
legislative co-sponsorship during their first term in parliament (respectively 1992-1994 and 2013-2018) and
the one they passed together in opposition (2013-2018)
