When will the Democratic Party ask itself why it is losing so many members?

[still_one]

150. Some people register as independent because their state has open primaries, where independents have

a choice between a Democratic ballot, a republican ballot, and and independent ballot. Those who are registered to a specific party do not have that choice in an open primary state.

Though you are correct that more have shifted to an independent status, it has happened more at the expense of the republican party than the Democratic party.:

Republican identification peaked at 34% in 2004, the year George W. Bush won a second term in office. Since then, it has fallen nine percentage points, with most of that decline coming during Bush's troubled second term. When he left office, Republican identification was down to 28%. It has declined or stagnated since then, improving only slightly to 29% in 2010, the year Republicans "shellacked" Democrats in the midterm elections.

Not since 1983, when Gallup was still conducting interviews face to face, has a lower percentage of Americans, 24%, identified as Republicans than is the case now. That year, President Ronald Reagan remained unpopular as the economy struggled to emerge from recession. By the following year, amid an improving economy and re-election for the increasingly popular incumbent president, Republican identification jumped to 30%, a level generally maintained until 2007.

http://www.gallup.com/poll/166763/record-high-americans-identify-independents.aspx

So a lot of that, as far as republicans are concerned, can be attributed to the disaster that was the bush years.

Within that same link:

"It should be noted that 47% of Americans identify as Democrats or lean to the Democratic party, and 41% identify as republicans or lean to the republican party, so even in spite of their registration, they still support one party over another."