The first issue here is that the Democratic Party cannot unilaterally do anything. Given that the Republicans control Congress (as of the date of this response), Democrats can only propose legislation; a majority of Congress, including people from both parties, are needed to actually pass it.
The next issue is that social policies that promote home ownership as opposed to affordable rental housing normally benefit the well-off rather than the poor. In reducing income inequality and improving the lives of the poorest Americans, promoting home ownership, although it appeals to voters and populist sentimentality, is not necessary good public policy. Home ownership actually makes people less mobile, limiting job access.
The key to making homes affordable does not lie in strategies such as mortgage subsidies (which benefit the rich and middle class rather than the poor) or subprime mortgages (which lead to bankruptcies) but in making sure that working people have adequate incomes.
One major cause of bankruptcies and home foreclosures in the United States is due to the high cost of medical care. Although the ACA was a good first step, moving to a single payer national health system, like that of Canada or Europe, would mean that illness would not bankrupt people and cause them to lose their homes.
The next important policy step would be some sort of minimum wage guarantee or income top up which would ensure that people could afford housing. When people are making $7.25 an hour (=$290/week or $14,900 a year), they are simply not able to afford housing in most parts of the country,
On a regional level, several effective programs have been started in areas that are losing population, including Detroit and some small midwestern towns, which involve giving away abandoned homes or land if people are willing to build on the property or repair the homes and live in the area for a minimum period. Perhaps the federal government could start a nation-wide registry making it easier for people (especially those without good internet research skills) to find out about such local programs and be matched with such houses. The difficult part of such a process though is that areas of declining population generally are losing people due to declining job opportunities. A program which made housing in such areas available would need to be supplemented by high-speed internet access and perhaps access to free education for jobs that could be done from remote locations over the internet.