Approval numbers for congressional Democrats are edging upward after several years in the cellar. So why are the favorability ratings of Senate Majority Leader Harry Reid and House Speaker Nancy Pelosi going down?

The Speaker's unfavorable rating jumped to 43 percent in a Diageo/Hotline poll released March 5, up from 34 percent at the end of January. And, for the first time this year, Daily Kos/Research 2000 polling shows Pelosi's disapproval rating eclipsing her approval rating, 38-42, in a poll conducted last week.

Reid has been sliding in public opinion polls as well. His favorable/unfavorable split was 18-27 in the March 5 Diageo/Hotline poll, down from an 18-20 split in the Jan. 28 poll. His 33-46 favorable/unfavorable split in a recent Daily Kos/Research 2000 -- a 13-point differential -- is his lowest of 2009 in that poll.

The Democratic leaders' waning support coincides with a marked uptick in public approval for Congress, whose favorability ratings had languished in the near-single digits until only recently. Thirty-nine percent of Americans back Congress, according to a March Gallup poll, up 20 points since January and the body's highest rating since February 2005. Pollster.com has tracked a consistent upward trend in congressional approval ratings beginning back in December.

The trouble area for both Democratic leaders has been independents; they have seen their unfavorable ratings among these voters jump by double digits since the beginning of the new Congress. Pelosi's unfavorable rating among indies jumped 12 percentage points to 45 percent, while Reid's negatives shot up 13 points to 30 percent.

Pelosi's slide continues a downward trend for the Speaker, whose approval ratings have slipped since Democrats took control of the chamber in early 2007. A lot of that has to do with the Republican base rallying against her, James Barnes explained in a recent article for National Journal.

"[Democratic pollster David] Beattie said that Pelosi's unpopularity is probably a function of her being Speaker, a position that is the personification of an institution rarely held in high regard," Barnes wrote. "Moreover, he noted that although Pelosi is likely to figure prominently in 'process' stories that detail the legislative sausage-making in the House, in local news stories on stimulus spending back in the districts she won't get a lot of credit."

Pelosi's unfavorable ratings still haven't climbed as high as those of former House Speaker Newt Gingrich, R-Ga., who topped 60 percent in 1997, Barnes noted. Pelosi's immediate predecessor, Illinois Republican Dennis Hastert, was a lower-profile figure, but even he rarely netted positive approval ratings during his tenure.

As for Reid, his dwindling public support is of more immediate concern: The National Republican Senatorial Committee is already gunning for his Senate seat in 2010. Reid handily defeated his under-financed Republican opponent in 2004, before he became majority leader, but narrowly squeaked by in the two races prior to that.