You regularly see this happening in France with votes for the Front National and Marine Le Pen. What tends to happen is the Far Right parties do quite well in

You regularly see this happening in France with votes for the Front National and Marine Le Pen. What tends to happen is the Far Right parties do quite well in the first round of voting, at which point the parties who have been eliminated cross political divides to encourage everyone to shun the Far Right. ( https://en.wikipedia.org/wiki/Cordon_sanitaire#In_politics https://en.wikipedia.org/wiki/Cordon_sanitaire#In_politics). It's hard to say whether, on balance, this is a useful exercise. The FN is able to use this approach to present itself as the voice of the 'anti-establishment' Party, everyone is able to use the first vote as a pressure valve to let off steam and vote FN knowing there won't be any consequences too it, and there's always the risk that voters tire of Cordon Sanitaire entirely and just vote the Far Right in in the second round anyway.