The part of the Constitution that enumerates the powers of Congress -- beloved of conservatives who wish to claim that any law they don't like exceeds the Constitutional writ -- is Article 1, Section 8. That article is one long sentence with multiple clauses, a few of which are below:
The Congress shall have Power To lay and collect Taxes, Duties, Imposts and Excises, to pay the Debts and provide for the common Defence and general Welfare of the United States; but all Duties, Imposts and Excises shall be uniform throughout the United States;
To borrow money on the credit of the United States;
...
To promote the Progress of Science and useful Arts, by securing for limited
Times to Authors and Inventors the exclusive Right to their respective Writings
and Discoveries;
To constitute Tribunals inferior to the supreme Court;
...
To declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water;
To raise and support Armies, but no Appropriation of Money to that Use shall be for a longer Term than two Years;
...
And so on.
Reading through this list, I realized something. This isn't just a list of powers. It's a list of duties.
Not only was Congress being given the power to do these things, the expectation was being written that Congress would do these things. A Congress that failed to establish post offices, or provide for the Army, or establish federal courts, or set up a patent office, would be derelict in its duty. The one exception -- we don't want the Congress constantly declaring war or granting letters of marque -- refers to a power to be exercised in discrete instances. The rest of the powers enumerate the ongoing responsibilities required to govern a nation. Section 9 lists acts Congress must not do; but no other section enumerates what it must do. Section 8, then, is what the Constitution expects of Congress.
But this means that the current crop of Congressional freshmen of the Tea Party Caucus has unilaterally abrogated the very first duty on this list: they refuse to exercise the power to lay and collect taxes. Many subscribe generally to a philosophy that views taxation as theft; all, up to the leadership, are refusing in the face of urgent need to raise the taxes the Government needs to exercise all the other duties listed in the section. If they refuse to do so now, then there is no situation whatsoever that could convince them to lay and collect a tax. In so refusing, they fail to fulfill the duties of Congress, and are thereby derelict.
Just a thought on interpreting the current situation. The problem we have with Tea Party Congressmen is that they don't entirely want to be Congressmen, because doing that would involve the hard parts of the job.