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(The Root) -- A Democratic source has confirmed exclusively to The Root that for the first time ever, first lady Michelle Obama will give the keynote address at the Congressional Black Caucus Foundation Phoenix Awards on Sept. 22.

With her husband tied up on the campaign trail, the first lady will be taking his place at an event that has become a regular stop on his calendar. As polls show the 2012 presidential election tightening, combined with concerns about an enthusiasm gap among 2008 Obama supporters and fears regarding the impact of voter-ID laws on the African-American vote, black Democratic legislators nationwide have emerged as crucial allies to the Obama 2012 campaign. The fact that the first lady is being entrusted with a solo speaking slot at such an important event in an election year speaks to her popularity and newfound political capital.

A Democratic source with close ties to the White House acknowledged that "in recent weeks she has solidified her popularity with the American people as one of the strongest voices within the administration on behalf of the president. This keynote address is indicative of that." The source also noted that they are not oblivious to the fact that she is currently more popular than the commander-in-chief.

The first lady is not the only one basking in the afterglow of a Democratic convention speech home run. Vice President Joe Biden, whose tough yet subdued performance in Charlotte, N.C., was widely praised by critics, will be keynoting the Congressional Hispanic Caucus Institute gala.

The one fact the source was tightlipped on? Which designer the first lady plans to wear. Her Michael Kors ensemble from last year's Phoenix Awards wowed the fashion set, while her Tracy Reese dress worn during her speech at last week's Democratic National Convention sparked a mob scene at the designer's fashion show Sunday during New York Fashion Week.

Keli Goff is The Root's political correspondent. Follow her on Twitter.

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