Editor’s note: David Frum writes a weekly column for CNN.com. A special assistant to President George W. Bush from 2001 to 2002, he is the author of six books, including “Comeback: Conservatism That Can Win Again,” and is the editor of FrumForum.

Washington (CNN) — The president’s approval numbers have sagged again, to just about the lowest point in his presidency. He’s trailed below 50% since the spring of 2010; now he’s sunk to 43%.

Bad poll numbers obviously create a vulnerability for an incumbent president. They also create a dangerous temptation for opponents to overplay their hand — as Democrats did in 2004 facing George W. Bush.

Bush’s approval rating had spiked to 90% in the aftermath of 9/11. Over the course of 2002 and 2003, his numbers returned to earth. By the fall of 2003, Bush had hit 50%, the lowest approval rating to that point in his presidency. Through 2004, Bush would struggle to remain north of 50%. To the amazement and disgust of Democrats, Bush heaved himself over the magic line just in time for Election Day.

David Frum

Democrats often attribute their unexpected defeat in 2004 to the negative campaign against their candidate.

That hurt for sure. Also true, however, was that the Democrats misjudged their affirmative campaign. They succumbed to their own anger and contempt for George W. Bush. As John Kerry put it in his 2004 speech accepting the nomination:

“I will be a commander in chief who will never mislead us into war. I will have a vice president who will not conduct secret meetings with polluters to rewrite our environmental laws. I will have a secretary of defense who will listen to the best advice of the military leaders. And I will appoint an attorney general who will uphold the Constitution of the United States.”

That’s a scorching indictment. It just happened not to be the indictment the American voter was waiting to hear in 2004 after three difficult economic years. The US economy produced 2 million new jobs in 2004 — but even so, fewer Americans were at work on Election Day 2004 than on Election Day 2000. Almost one-half of the new jobs of 2004 were claimed by foreign-born workers, many of them illegal. Perhaps as a result, wages for nonsupervisory workers actually declined in 2004 even as payrolls grew.

If the Democrats had credibly focused on that issue — if they had nominated a candidate who spoke about wages with the same intensity and conviction that Kerry spoke about Iraq — the election might have had a very different result.

Flash forward to 2011.

Republican partisans loathe Barack Obama even more viscerally than core Democrats despised George W. Bush. Yet as with Democrats in 2004, it’s hard for Republicans to keep in mind: The typical voter does not feel as they do.

Even now, only 48% of Americans blame Barack Obama for the state of the economy, as opposed to 71% who blame George W. Bush.

Even now, Americans continue to show considerable personal support for Barack Obama, even as the Republican brand remains toxic, with 68% disapproving of the job Republicans are doing in Congress.

The message for Republicans in these polls would seem to be: Fight the plan, not the man. Americans may be persuaded that Obama is a basically decent guy, in over his head. They won’t be persuaded that Obama is an anti-American radical on a jobs-destroying rampage.

And yet it is precisely that kind of implausibly angry anti-Obama talk that Republican primary voters delight to hear. Texas Gov. Rick Perry has displaced Mitt Romney as the Republican front-runner by offering Republicans a stronger anti-Obama message. As for Perry’s own vulnerabilities — vulnerabilities that get bigger every time the Texan unburdens himself of new qualms about Social Security and Medicare — Republicans gripped by anti-Obama emotion just cannot see them, any more than Democrats could see John Kerry’s disconnect from the economic concerns of middle-class voters.

Partisans love a fighter. They want a candidate who expresses strong feelings in strong language. It’s very difficult for them to remember that less partisan Americans have different feelings — and that for every American who regards Obama with anger and dislike, there are perhaps two Americans who regard him with regret.

If the Republican presidential nominee can connect with voters’ feelings of disappointment in Obama, he or she may find a way back to the White House. If the nominee expresses the rage of the Republican base, he or she will only alienate the much larger number of voters to whom that rage is alien and off-putting. The challenge for Republicans in 2012: Before they can defeat Obama, they must first overcome themselves.