You can't get your arms around a public mood. Nor can you bottle it, can it, dust it off or cram it into a vase. What you can do is try to sense it, like now, as growing numbers of Americans show themselves ready for a change of magnitude: a plague-o'-both-your-houses kind of change.

The Obama boom was the first sign, sounding loudly from the left. From the right comes the Thompson boom, loud echoes of which I picked up at a conservative parley over the weekend.

Obama. Thompson. Where'd they come from all of a sudden? What about Clinton? What about McCain?

As we learn quickly enough in politics, public moods can pass like clouds before the sun. It may be that next year will find Democrats coming home to the familiar, typified by the celebrated wife of their last president. Republicans may find in John McCain or even Rudy Giuliani -- Mitt Romney would be another story -- the comfort no newcomer can provide. For now, it looks increasingly like Barack Obama vs. Fred Thompson?

Someone on the website of the Sunday Times of London a few days ago put it in nonpartisan fashion: "Let's have some new blood in our political system. Obama or Fred Thompson could be a good start." Obama, so I gather, as the voice of new directions and answers; Thompson as the standard bearer of time-tested ideals. The goals hardly meld, but the inclination to choose one or the other has common origins. It arises from feelings of intellectual sterility -- worn-outness, not just with the Iraq war, but with the cacophony of the moment.

"Nobody likes anybody else" seems the perception of the moment. If anything, we seem to despise each other. Those of us who have been around for a while suggest that political and cultural divisions haven't been this deep since the '60s. Obama's and Thompson's putative appeal likely has less to do with their barely discernible programs than with the hope that they might lead us beyond our present squabbles.

As a political conciliator, Obama shows gifts possibly equal to Bill Clinton's. As president, he'd well, how many Democrats care profoundly? He'd be different. Likewise, our first white/black president would challenge us in as yet unspecified ways.

Thompson, whose name conservatives are rolling pleasantly around in their mouths, is said to be the real Reagan conservative. Beats me. I had to scratch my head to come up with the name of his TV show. Yet old Reaganites are gaga over him. Thus Michael Deaver: "[Thompson] could change this whole thing and turn this primary system upside down." Thus Roger Stone: "The president Americans want is, in fact, the guy they see on 'Law and Order': wise, thoughtful, deliberate, confident without the cockiness of George W. Bush, urbane yet country."

Here we go again, maybe, on the path twice blazed by Ross Perot. Perot's merit didn't lie in what he might do as president. It lay in his differentness. He was new. New was what enough Americans wanted that it cost George H. W. Bush the election of '92. By '96, new was old.

I am not sure whether the Obama-Thompson obsession speaks worse of our feverish natures than it does of candidates Clinton, McCain and so on. Patience isn't the characteristic virtue of modern democratic societies wedded to the notion that no problem is so bad it can't be fixed overnight; no division so wide it can't be closed by daring personal intervention.

The tragedy of history -- i.e., the same anxieties, the same hatreds, the same futilities hanging around forever, always taking on new forms -- isn't something we talk about much in the age of tummy tucks and iPods, when satisfaction looks utterly possible, if only...

I wouldn't challenge the electoral prospects of Obama or Thompson, either one. I wouldn't give odds, either, on the nation's mood after 12 or 24 months' experience with -- I don't know what else to call it -- reality.