Vice President Kamala Harris’ campaign unveiled an ad Tuesday showcasing her proposal to make homeownership more affordable for Americans as she makes her housing plan the centerpiece of her economic agenda.

The new minute-long ad, narrated by Ms. Harris, tells her personal story of growing up in rental housing while her mom saved for a decade to buy a home. 

“I was a teenager when that day finally came, and I can remember so well how excited she was,” Ms. Harris says in the ad. “I know what homeownership means, and sadly right now it is out of reach for far too many American families.”

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The ad, titled “Full House,” targets voters in swing states, including Arizona and Nevada. It’s part of the Harris campaign’s $150 million media buy for August. 

Ms. Harris has proposed offering $25,000 in government funding to first-time homebuyers and building 3 million more housing units in four years on top of the roughly 1 million homes built annually by the private sector. 

Housing costs have been one of the main drivers of inflation, rising 5.1% the past year, compared with overall inflation’s 2.9% increase, according to the Bureau of Labor Statistics.

“Vice President Harris knows we need to do more to address our housing crisis; that’s why she has a plan to end the housing shortage,” said Dan Kanninen, the campaign’s battleground state director.

Ms. Harris’ plan would offer tax breaks for homebuilders and broaden incentives to spur increased rental housing construction. She would double the available funding to $40 billion to encourage local governments to remove red tape that prevents additional construction and offer first-time buyers $25,000 in tax credits.

The Committee for a Responsible Federal Budget, a nonpartisan spending watchdog, said Ms. Harris’ proposal would cost at least $200 billion over 10 years. 

It’s also unclear if Ms. Harris would be able to push those policies through Congress. President Biden has offered similar proposals that have failed to clear Capitol Hill. 

Former President Donald Trump has offered several ideas to lower housing costs, including cracking down on illegal immigration to reduce demand.

“I will also stop inflation by stopping the invasion, rapidly reducing housing costs,” Mr. Trump said at a June campaign rally.

Mr. Trump has also proposed the possibility of opening up more federal land for home construction and has spoken out against loosening zoning restrictions that prevent apartments and affordable housing from being built in single-family home neighborhoods. 

“I keep hearing about the suburban woman doesn’t like Trump,” he said last week in Michigan. “I keep the suburbs safe. I stopped low-income towers from rising right alongside of their house, and I’m keeping illegal aliens away from the suburbs.”