President Obama's speeches often claim "the time has come" for something, or "the days" of this or that "are over." It's as if his presidency has introduced a new epoch.

I used to think that invoking the vision of a new age was merely a rhetorical device to distinguish him from George W. Bush. Now I think it is something more - a way to make a very old philosophy sound new and failed policies of the past seem fresh and exciting.

The trope was in full view last week when the president spoke before the U.N. General Assembly. "The time has come to realize that the old habits, old arguments, are irrelevant to the changes faced by our people," he intoned. But when he got around to presenting his new arguments and ideas, they sounded rather familiar.

Every policy and theme outlined in the president's speech has been tried; most have failed. They only appear fresh because their failure happened so long ago that some of us have forgotten and others who don't know history think them untried.

Take Mr. Obama's "comprehensive agenda" to rid the world of nuclear weapons. This dream is as old as the first atomic bomb explosion. Arms control agreements have failed so many times, it's hard to keep track of the failures. Despite all these agreements, North Korea and Pakistan managed to get their own nuclear weapons, and Iran is close behind.

Mr. Obama would have us believe that nukes have proliferated due to (a) a lack of good faith gestures by America (i.e., unilateral disarmament) and (b) a need for new agreements. But the problem with North Korea and Iran, who are merely the worst proliferators, is not the lack of agreements but their failure to live up to those they've signed.

Don't get me wrong. When arms control negotiators are hard-headed, as Ronald Reagan was, agreements can be beneficial. The trouble starts when you can't tell friend from foe, and you assume America is as much a part of the problem as, say, North Korea. In this version of "blame America," Mr. Obama's arms control approach is a throwback to the days of Jimmy Carter's failed Strategic Arms Limitation Talks and Bertrand Russell's Campaign for Nuclear Disarmament (CND) of the 1950s. The real disarmament target of the CND was not rogue states but the United States and Western powers.

Another already-tried idea of the president's is "engagement," which appears in many forms. It was particularly prominent in the U.N. speech, when he said he has "re-engaged" by joining the disappointing U.N. Human Rights Council.

Engagement is one of those words diplomats love, often adorned with such clever modifiers as "selective" and "constructive." It can mean practically anything, but it sounds good because, whatever it is, it's not war or conflict.

The hallmark of Mr. Obama's engagement strategy was Iran. The sheer act of offering to talk was supposed to convince the Iranians to give up their nuclear program. It didn't work. His Iran policy came crashing down last week when yet another secret nuclear site was discovered. He discovered what Mr. Bush learned when he and the Europeans repeatedly offered negotiations to the Iranians: They prefer to keep their program regardless of the incentives we offer.

Engagement should be a means to an end, not an end in itself. If circumstances are ripe for negotiations, by all means, negotiate. But if they are not, don't pretend that repeatedly offering diplomatic talks and getting nothing in return will change anything. For countries like Iran and North Korea, the problem is not that we don't respect them, but that they want something we don't want them to have - namely, nuclear weapons.

If you value engagement more for what it promises, as Mr. Obama does, rather than what it delivers, then you will often err on the side of letting things slide. You can always excuse delay and deferral of solving hard issues because the cost of acting appears to be greater and riskier than no action. The problem, of course, is that sometimes no action is the riskiest strategy of all, as we saw in the years of neglect of al Qaeda that led up to Sept. 11.

This is a hard lesson of history. But if you make a virtue of forgetting that history, which is the president's habit when he makes exaggerated claims about the benefits of engagement, then you not only lose a record of what has worked and what has not worked. You also lose a balanced view of what is possible and what is not.

A little modesty is in order, Mr. President. The "time has come," indeed, not for recycling failed policies of the past, but to drop the pretense of ushering in a "new" age, which didn't work out so well the last time it was tried.

Kim Holmes is vice president of foreign- and defense-policy studies at the Heritage Foundation and author of "Liberty's Best Hope: American Leadership for the 21st Century."