A whiplash-inducing turn of events has seen Italy's president (who is not popularly elected) veto a government proposed by the populist Five Star and League parties and ask an ex-IMF economist to form a government.

Why it matters: Italy has now had a series of prime ministers take office without winning a popular mandate at the ballot box, dating back to Silvio Berlusconi's ouster in 2011. Current president Sergio Mattarella's drastic steps have sparked a debate over whether he is overruling the will of the people, or acting within constitutional bounds.

How it happened: Law professor and political novice Giuseppe Conte was put forth for prime minister last week by the populist parties, which performed best in the topsy-turvy March 4 election.

• Conte's proposed cabinet included 81-year-old eurosceptic economist Paolo Savona as finance minister. Mattarella said he couldn't accept a minister who advocated for leaving the euro.
• Conte abandoned his attempt to form a government, and Mattarella settled on Carlo Cottarelli, whose politics could hardly be more different.
• The populist parties want to block his appointment, and impeach Mattarella. Cottarelli, meanwhile, says fresh elections will be held early next year.

Correction: This article previously referred to Berlusconi as Sergio, rather than Silvio.