Three weeks after losing a national election, Italian Prime Minister Silvio Berlusconi has finally conceded the vote. His decision to step down eliminates one headache for the winner, Mr. Romano Prodi, but it is not the most important challenge the prime minister-to-be faces.

Rather, Mr. Prodi must wrestle with a fractious coalition that could shatter at any moment -- a prospect that was painfully clear during votes to select a president of the Senate, the upper house of the Italian Parliament. Political instability looms over Italy once again. Much-needed economic reform is unlikely and Mr. Berlusconi will do his best to exploit unhappiness and engineer his return to power.

Mr. Prodi, a former prime minister and former president of the European Commission, leads a center-left coalition that narrowly defeated Mr. Berlusconi in elections held last month. The margin of victory in the Senate races was razor-thin: less than 25,000 votes out of 38 million. Mr. Berlusconi alleged fraud and refused to concede defeat, even as his allies accepted the result. Some suggested that the prime minister's language was designed to inflame public sentiment and delegitimize Mr. Prodi's government. Sadly, he might not need any help on that front.