THE BURNED OVER DISTRICT

He left the Democratic party in 2000 and became a Republican of Convenience to take over NYC as its mayor. He has since gone Independent and in has announced his choice for President.

Michael R. Bloomberg, who bypassed his own run for the presidency this election cycle, will endorse Hillary Clinton in a prime-time address at the Democratic convention and make the case for Mrs. Clinton as the best choice for moderate voters in 2016, an adviser to Mr. Bloomberg said.

The news is an unexpected move from Mr. Bloomberg, who has not been a member of the Democratic Party since 2000; was elected the mayor of New York City as a Republican; and later became an independent.

But it reflects Mr. Bloomberg’s increasing dismay about the rise of Donald J. Trump and a determination to see that the Republican nominee is defeated.

Mrs. Clinton is seeking to reach out to middle-of-the-road swing voters and even moderate Republicans uneasy about Mr. Trump. Polls show that significant numbers of Republicans remain wary of Mr. Trump, and question his fitness for the presidency.

Mr. Bloomberg will vouch for Mrs. Clinton “from the perspective of a business leader and an independent,” said Howard Wolfson, a senior adviser to Mr. Bloomberg.

Mr. Bloomberg, who has been sharply critical of Mr. Trump’s views on immigration and the economy, may fortify Mrs. Clinton’s appeal to the political center.

And with the Republican nominee basing his campaign on his background as a businessman, Mr. Bloomberg, a billionaire media executive and philanthropist, may help counter the Trump sales pitch.

It is unusual, but not unheard of, for a speaker who is not a member of a political party to address that party’s convention. Mr. Bloomberg is expected to speak on Wednesday, the same evening as President Obama and Vice President Joseph R. Biden Jr.

Mr. Bloomberg and Mrs. Clinton are not personally close, but had a positive working relationship when he served as mayor and she as a senator from New York.

I am not sure why this is unexpected. Bloomie may be rapacious but he does follow a code of conduct most of us would be familiar with. And there was never any love lost betweenhim and The Great Orange Fungus.