Now Barack Obama has to figure out how to govern a country that is facing two draining wars abroad, a dismal fiscal picture at home and countless unmet needs, from uninsured children and unemployed workers to demanding retirees and deteriorating infrastructure.

Two ideas should guide the president-elect’s decision-making: investments and interest groups. He has to embrace the first and reject the second. He has to spend limited resources in careful ways that save money down the line and create jobs and wealth. And he has to stand up to the special pleaders who pressure the government to serve their own narrow constituencies.

In short, he has to revive a concept that sounds corny but is actually critical: the national interest. President Bush ran as a “uniter not a divider” but did not govern that way. Obama has to make good on his promise to end the destructive partisanship — practiced by Democrats as well as Republicans — that dominates the capital today.

Despite the Democrats’ impressive victory, only 22 percent of the voters called themselves liberals (34 percent identified as conservatives and 44 percent as moderates). Arizona Republican Jeff Flake predicted in the Washington Post that, “As surely as the sun rises in the east, the Democrats will overreach.” Obama’s task is to prove him wrong.

During his first year in office, Obama could face a budget deficit approaching a trillion dollars. That means he has to choose spending targets carefully and avoid the “redistributionist-in-chief” label John McCain tried to pin on him.

One good example of a wise investment: expanding health insurance for children. President Bush vetoed attempts to raise the current program from $5 billion to $12 billion, but every dollar spent vaccinating a child or detecting a chronic condition pays for itself many times over when kids stay out of emergency rooms and parents stay in the workforce.

Promoting green technology, through generous research credits, would also be taxpayer money well spent. Writing in Newsweek, New York Mayor Michael Bloomberg put it this way: “America can either be the pioneers of green energy or the purchasers. If we are the pioneers, we’ll create thousands of good paying jobs. If we are the purchasers, we will continue transferring billions of our wealth overseas — and high-tech jobs that go with them.”

Not all investments cost money. A particularly stupid government policy limits to 65,000 a year the number of H-1B visas issued to well-educated immigrants who want to contribute their energy and entrepreneurial spirit to this country. Obama should move quickly to raise that ceiling. As Microsoft founder Bill Gates told Congress, the “smartest people want to come here, and that’s a huge advantage to us, and … we’re turning them away.”

In aiming at the national interest, Obama will be confronted by resurgent Democratic power blocs, bursting with pent-up demands after eight years out of power. Front and center will be organized labor, eagerly promoting a measure that would make it easier to organize workplaces and extract contracts from employers.

Yes, real wages have slumped in recent years, but picking this fight right away could be a big mistake, Obama’s version of Bill Clinton’s decision to recognize gays in the military — a distracting battle that gets his administration off to a highly partisan and poisonous start.

More important is what Obama does on trade. Unions keep pushing Obama to renegotiate existing trade pacts and oppose new ones, when, in fact, expanded trade is absolutely essential for future economic growth. McCain estimated that 1-in-5 American jobs depends on trade and Richard Haass, president of the Council on Foreign Relations, wrote in Newsweek that a new global trade pact would spur growth by 1 percent annually and provide “the best noninflationary, anti-recession tool for the American and global economies.”

Not all interest groups are outsiders. Farm state lawmakers from both parties will continue to pressure Congress for outrageous agricultural subsidies. And many legislators, with a few notable exceptions, will greedily pursue the practice of “earmarks,” which direct federal funds to their districts regardless of any real benefit.

But money is not the only issue. Obama has to bring a new mindset to the job. He has to mean what he said on election night, that he wants to “heal the divides that have held back our progress.” For years now, the first question anyone asked in Washington has been: Does it help my party? The new president has to ask a new question: Does it help my country?