There are some rules which are so important that even people who are in a different profession know them.
In politics the first principal is: "Secure your base."
In medicine the obligation taken by physicians to "First, do no harm" is known to everyone (incorrectly) as the central theme of the Hippocratic Oath.
And, of course, in space travel, the Prime Directive of Star Fleet Command is to never interfere with an alien culture ("alien" in this usage refers to someone who is a Ferengi, not someone who is a Mexican).
Both the national Democrats (as represented by the Congressional leadership) and the national Republicans (as represented by the White House) are ignoring and/or violating the first principle of politics by actively supporting policies which are abhorred by their parties' bases.
The Dems are driving a wedge between Washington and the Liberal base over funding for Iraq. Putting aside the policy issues, there was no procedural reason for House Speaker Nancy Pelosi (D-Cal) and Senate Majority Leader Harry Reid (D-Nev) to continue to send funding bills to the President with a timetable for withdrawal.
The Left Wing of the Democratic Party - its base - is very vocal in its opinion that Pelosi, Reid, et. al. surrendered to President Bush on the war funding bill.
On the other side of the aisle, the White House is vociferous in its support of a massive change to the nation's immigration policy which the Right Wing of the GOP sees as nothing less than amnesty for the 12-20 million aliens illegally in this country. (In this usage "aliens" means people who are Central Americans not Klingons).
Thus, the Bush Administration is driving a wedge between the national policy structure and the GOP's political base.
Neither Bush, nor Pelosi, nor Reid are running for President. The 327 people who ARE running on each side might well see this as an opportunity to adopt an "I'm Not Them" posture ("Them", in this usage, refers to the alien beings in Washington, DC, not Romulans in the Beta Quadrant of the Milky Way Galaxy).
Democratic candidates for President are expected to oppose the policies of President Bush. This is much easier when the President appears to be stuck in the low- mid-thirties in terms of job approval.
Job approval numbers for Congress - controlled, you may have read, by Democrats - are just about as dismal as job approval numbers for the President.
Among the major polls taken during the merry month of May Pelosi/Reid's numbers range from a high of 36% (CBS/NY Times) to a low of 29% (Gallup).