Editor's note: David Frum writes a weekly column for CNN.com. A special assistant to President George W. Bush in 2001-02, he is the author of six books, including "Comeback: Conservatism That Can Win Again," and is the editor of FrumForum.

Even if he were to serve eight years in office, Barack Obama has likely already made all the most important decisions of his presidency. That's the nature of the presidency: The big decisions almost always come early, and then the president must live with them for better or worse.

A president can sometimes reverse course, as Bill Clinton did after he lost Congress in 1994. But while that reversal preserved Clinton's popularity, it destroyed his leadership. He spent the next six years presiding over a government whose course was steered from Capitol Hill, not the White House.

But big decisions seldom go right or wrong immediately. There are often months or even years of waiting for the outcome. And on four of his big decisions, President Obama is waiting now.

Decision 1 was the president's stimulus plan: a bet that $787 billion in borrowed money would cushion and shorten the worst recession since World War II.

Decision 2 was to let the banking industry recuperate on its own sweet time. During the Swedish banking crisis of 1993, the government put troubled banks into receivership at once, then quickly relaunched them with clean balance sheets so that they could resume lending. Obama has chosen a different course; less radical, but also with a slower recovery time.

Decision 3 was to send 30,000 additional troops to Afghanistan.

Decision 4 was to "go big" on health care -- to enact a sweeping reform rather than fix problems one by one.

As yet, we cannot deliver a final assessment of any of these decisions, although the early returns on decision 1 do not look very favorable.

Like the president, the nation is waiting, too.

More to the point, Obama is waiting for the electorate's verdict.

The hardest part of the presidency is the waiting. Over the course of a presidency, a president will make thousands of decisions. Only a very few will determine whether a presidency succeeds or fails. And oftentimes, the interval between the decision and the result is measured in months.

We honor those months of waiting when the decision turns out well: Lincoln pacing as he waited for news from Gettysburg, Vicksburg or Atlanta.

Oblivion closes over the long months of waiting for a less positive result: Lyndon Johnson waiting for light at the end of the tunnel in Vietnam, Richard Nixon waiting for Americans to grow weary of Watergate, Jimmy Carter waiting to hear whether his overtures to the Iranian mullahs would liberate U.S. hostages, George H.W. Bush waiting for an economic recovery to materialize in time to win the 1992 election.

Presidents tend to be men of optimistic temperament. (Think of Ronald Reagan's joke about the boy shoveling through a mountain of horse manure: "There has to be a pony in here somewhere!") But well before the final disaster arrives, a president has to sense that things are not trending in his direction.

Nearly 18 months into the Obama presidency, the banking system still staggers under bad debt, jobs are not being created in substantial numbers, the news from Afghanistan continues to be bad, and economists are revising the projected cost of the health care plan up and up.

The stimulus plan has protected public-sector employees from layoffs, but it has not sparked private-sector job creation.

In a speech this past week, Sheila Bair, head of the Federal Deposit Insurance Corp., said that 11 million American homes are worth less than the value of their mortgages. So while (good news) "only" 2.4 million American homes are currently in foreclosure, another 8.5 million could follow any time their owners get sick of owing more than their home is worth.

In Afghanistan, it's fair to say that nobody is an optimist. The generals and the troops do their work professionally, often heroically, but just ask them if they believe the mission will succeed and listen to them hedge and hem.

As for the health care plan, things are deteriorating before our eyes. Despite promises that people who like their plans will be able to keep them, the administration's own regulators acknowledge that 51 percent of workers will discover changes in their health coverage as a result of the health care bill.

It's too early to pronounce definitively that the big Obama decisions are not working. Obama defenders will say Reagan was not looking too good at the 18-month mark either and still persevered to ultimate success. That's true.

It's also true that Herbert Hoover and Jimmy Carter looked bad at 18 months, only to look even worse at 48 months.

In the wonderful phrase of the novelist David Eddie, "They laughed at the Wright brothers. Of course, they also laughed at all the people before the Wright brothers, the ones who jumped off cliffs frantically waving their wooden wings or clutching their propeller beanies."

The opinions expressed in this commentary are solely those of David Frum.