MCCAIN’S SUPPORT FADES, OBAMA TAKES SOLID LEAD…. All the usual caveats still apply — a lot can happen in six weeks; national polls are primarily interesting for little more than trend lines; a presidential race is a state-by-state contest; and it’s best not to invest too much energy into just one poll.

That said, Democrats who were white-knuckling the campaign a couple of weeks ago are probably feeling a little more encouraged right now.

Gallup reported earlier this month that recent history shows that the candidate leading after the second convention holds onto the national lead for at least a month, even after the convention bounces fade. “[I]f Obama regains the lead over the next month,” Gallup reported on Sept. 9, “he will be bucking the historical trend.”

As it turns out, that’s what has happened.

Turmoil in the financial industry and growing pessimism about the economy have altered the shape of the presidential race, giving Democratic nominee Barack Obama the first clear lead of the general-election campaign over Republican John McCain, according to the latest Washington Post-ABC News national poll.

Just 9 percent of those surveyed rated the economy as good or excellent, the first time that number has been in single digits since the days just before the 1992 election. Just 14 percent said the country is heading in the right direction, equaling the record low on that question in polls dating back to 1973.

More voters trust Obama to deal with the economy, and he currently has a big edge as the candidate who is more in tune with the economic problems Americans now face. He also has a double-digit advantage on handling the current problems on Wall Street, and as a result, there has been a rise in his overall support. The poll found that, among likely voters, Obama now leads McCain by 52 percent to 43 percent. Two weeks ago, in the days immediately following the Republican National Convention, the race was essentially even, with McCain at 49 percent and Obama at 47 percent.

As a point of comparison, neither of the last two Democratic nominees — John F. Kerry in 2004 or Al Gore in 2000 — recorded support above 50 percent in a pre-election poll by the Post and ABC News.

A couple of other angles to consider from this poll — first, Sarah Palin’s poll numbers are fading, with her unfavorable rating going up 10 points in two weeks. The percentage of independents with favorable views of Palin dropped from 60% to 48% over the same time frame, including a huge 18-point drop among independent women.

Second, the “enthusiasm gap” seems to have reemerged — 62% of Obama supporters are “very enthusiastic,” while 34% of McCain’s backers said the same. Immediately after the Republican convention, about half of McCain’s supporters were “very enthusiastic.” What’s more, the Post noted, “Among Republicans, conservatives and white evangelical Protestants, strong enthusiasm for McCain’s candidacy has dropped by double digits.”

And third, independents now prefer Obama by a wide margin, 53% to 39%, and Obama’s advantage among independents on the economy is now a whopping 21 points.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.