The man New York Democrats seemed poised to choose this week as their candidate for mayor, Bill de Blasio, sure has a lot in common with President Obama.

Both men were born in 1961. They both describe their fathers as alcoholics and say they were brought up primarily by their mothers and their mothers’ families. Both politicians have degrees from Columbia University and once lived in Cambridge, Mass. They both once lived under different names — Mr. Obama as Barry Soetoro and Mr. de Blasio as Warren Wilhelm Jr., the name he was born with.

They both have ties to the far left New Party; de Blasio reportedly worked as executive director of the New York branch of the New Party, while documents indicate that Obama joined the Chicago New Party and signed its candidate pledge. Both Messrs. Obama and de Blasio are married to black women they met at work.

Beyond the biographical coincidences, and more importantly, the two politicians seem to be following the same political and policy playbook. They want to raise taxes on the rich to fund health-care and education sectors whose government-spending-reliant growth they are unwilling to restrain. While for Mr. Obama and perhaps Mr. de Blasio, that’s been a path to political success, or at least election and re-election, it’s a policy that also comes with considerable costs and risks.

Mr. De Blasio’s signature policy proposal is an income tax increase for New York City residents who earn more than $500,000 a year, with the proceeds directed to public education. President Obama ran on asking “millionaires and billionaires” to pay higher taxes, in part to fund his ObamaCare subsidies for health insurance.

But Mr. de Blasio likes health care spending, too. He’s been fighting to keep city hospitals open, even if there’s insufficient patient demand to support them. And Mr. Obama likes education spending, too; he has ramped up Pell Grant spending and called in a State of the Union speech for exactly the expanded pre-kindergarten programs that de Blasio is campaigning to bring to New York.

Mr. De Blasio has backed an increased minimum wage at the local level, just as President Obama has supported one nationally. Mr. De Blasio has used his teenaged son in a campaign commercial against the New York Police Department’s “stop, question, and frisk,” tactics, while President Obama famously said, after the fatal shooting of Trayvon Martin in Florida, “If I had a son, he’d look like Trayvon.”

Messrs. De Blasio and Obama both have scant private-sector experience, which may account for their tendency to see successful businesspeople as cows to be milked for the maximum possible tax revenue. Mr. Obama’s ambitions have been somewhat limited by Republicans in Congress, while Mr. de Blasio, if he wins the primary and the general election that follows, will be constrained, at least somewhat, by Republicans and more conservative Democrats in Albany.

The final constraint on a Mayor de Blasio, however, won’t be merely some other politicians in Albany; it will be the reality that a tax, spend, polarize, and regulate approach to government inevitably confronts. It’s wasteful, it’s expensive, it doesn’t function particularly well, it breeds corruption and resentment, and eventually the people who are being taxed to excess decide to stop participating, either by moving or by restructuring their affairs so as to generate less taxable revenue (and usually fewer jobs, too).

President Obama does have some tools Mr. de Blasio will lack, among them the ability to print money and the ability to conduct foreign policy in a way that distracts from domestic problems. If Mr. de Blasio governs as he has campaigned, though, don’t be surprised if in a few years he finds himself wishing he could ask the City Council for the authority to attack New Jersey.

Mr. Stoll is editor of FutureOfCapitalism.com and of Smartertimes.com.