if the Conservatives do pick it up, it means that the riding will have voted for four different parties in four straight elections. Has that ever happened before?
The federal riding of Louis-Hébert in the last four elections.
2006 Conservative
2008 Bloc Québécois
2011 NDP
2015 Liberal
https://en.wikipedia.org/wiki/Louis-H%C3%A9bert_(electoral_district)
Not only that but Louis-Hebert also changed hands in 2006 (BQ -> Con), 2004 (Lib -> BQ) and 2000 (BQ -> Lib) such that it has changed parties at each of the last
seven federal elections. I don't think any other seat comes close. It's also elected a different, non-incumbent MP at each of the last
nine federal elections, since the BQ MP first elected in 1993 stood down in 1997 and was replaced by a different BQ MP, which must also be a record. There's a reasonable chance the Conservatives gain it back at the next election, too, which would continue the pattern.