Michael Bloomberg, the billionaire former Republican mayor of New York City, is backing Hillary Clinton. He took aim at Donald Trump’s business record in his DNC speech, saying the Republican nominee has left bankruptcies, lawsuits and angry stockholders in his wake. Photo: Getty Images. By Josh Dawsey Josh Dawsey The Wall Street Journal CANCEL Biography @jdawsey1 Joshua.Dawsey@WSJ.com Updated July 27, 2016 10:36 p.m. ET 242 COMMENTS PHILADELPHIA—Billionaire businessman Michael Bloomberg delivered a stinging rebuke of GOP presidential nominee Donald Trump at the Democratic National Convention Wednesday night, calling him a “dangerous demagogue.” “Trump says he wants to run the nation like he runs his business. God help us,” said Mr. Bloomberg, a former New York City mayor who is unaffiliated with any political party. “I’m a New Yorker. I know a con when I see one.” Mr. Bloomberg said there is “no doubt in my mind” that Democratic nominee Hillary Clinton is the “right choice” in the Nov. 8 election. He told fellow independents that their votes mattered and he urged the nation to “elect a sane, competent person with international experience, a unifier.” “Hillary Clinton understands this isn’t reality television,” he said. “This is reality.” A spokeswoman for Mr. Trump didn’t immediately respond to a request for comment. Mr. Bloomberg, 74 years old, may have seemed like an unlikely political figure to address the Democratic convention during a year when the party’s left-wing activists are protesting Mrs. Clinton for being too establishment and cozy with Wall Street. More on Election 2016 Bill de Blasio Attacks Donald Trump in Convention Speech July 27, 2016 Gov. Andrew Cuomo Faces His Critics at Democratic Convention July 27, 2016 De Blasio Seeks a National Reboot July 26, 2016 Democrats in Albany Skeptical of Cuomo’s Support July 25, 2016 Bratton’s Exit Challenges Mayor July 25, 2016 But aides to Mr. Bloomberg said his remarks weren’t focused on the crowd in the convention hall. Instead, his remarks were designed to influence moderates at home and send a message that voters should unite against Mr. Trump, a fellow New York billionaire. During his speech, Mr. Bloomberg said he sometimes disagreed with Mrs. Clinton and believed the Democratic Party had sometimes demonized the private sector and blocked necessary changes to schools. But he said it was imperative that voters elect Mrs. Clinton. The next president should be a problem solver, not a bomb thrower, he said. Mr. Bloomberg, who worked on Wall Street before founding his eponymous financial communications company, sees a distinct opportunity to jump into the 2016 fray, his aides said. But it remained unclear Wednesday how heavily he will campaign for Mrs. Clinton. Mr. Bloomberg’s spin on the national stage comes months after he publicly weighed a run for president but determined that he couldn’t win as a third-party candidate. He also weighed a run in 2008 but decided against it. “There’s always a little regret, but he doesn’t dwell on it,” said Democrat Ed Rendell, a former governor of Pennsylvania and a friend. Mr. Bloomberg was a lifelong Democrat before he became a Republican in advance of his first campaign for mayor in 2001. Mr. Bloomberg left the GOP in 2007 as he flirted with running for president. In 2009, when he successfully sought a third term as mayor, he ran as the GOP nominee. As a presidential candidate, Mr. Bloomberg would have struggled in many states because he is known for his pro-gun control positions and his controversial (and unsuccessful) proposal to ban large , sugary drinks in New York City, political observers said. For many supporters of U.S. Sen. Bernie Sanders of Vermont, who railed against Wall Street and lost the Democratic primary to Mrs. Clinton, Mr. Bloomberg isn’t an ideal presidential candidate. Mr. Bloomberg has been a longtime advocate for Wall Street. “God bless him but he never would have made it” to the White House, said Bill de Blasio , who succeeded Mr. Bloomberg as mayor and is supporting Mrs. Clinton, during a breakfast in Philadelphia Wednesday. ENLARGE Mr. Bloomberg’s spin on the national stage comes months after he publicly weighed a run for president but determined that he couldn’t win as a third-party candidate. Photo: Aaron P. Bernstein/Getty Images New York City Councilman Ritchie Torres, a Bronx Democrat, said: “Bloomberg has the politics of a centrist Democrat with an even sharper bent toward Wall Street—his politics are out of sync with the zeitgeist of the Democratic Party.” Mr. Bloomberg isn’t personally close with Mrs. Clinton but knows her from his time in government, aides said. The former mayor endorsed Republican George W. Bush in 2004 and Democrat Barack Obama in 2012; he didn’t make any endorsement in 2008. Inside…