The budget deal struck on Friday night is historic as a substantive matter. But it is also a useful tool in separating who is credible and who is not on both the right and left.

On the Democratic side you have the president, his flacks, the Democratic National Committee and a few others who see the deal as a big “win” for President Obama.When the White House sends David Plouffe rather than a serious policy adviser on “Meet the Press” and “Fox News Sunday,” you understand that the White House is in spin mode. And how preposterous is the spin that a continuing resolution with significant cuts Obama had opposed, which was struck with zero assistance from the White House, is a reflection of his leadership. Are we supposed to take seriously Plouffe’s line that Obama intended all along to “not get engaged” in the back-and-forth? You understand the game here is to justify a strategy of do-nothingism. Maybe that is why Obama signed the CR in private, with no press or fanfare.

But there is silliness on the Republican side as well. You hear a few hard-line congressmen proclaim that House Speaker John Boehner (R-Ohio) didn’t get “enough” or that a shutdown would have been a win for the Republicans. These are the voices of the perpetually aggrieved on the right who will oppose any deal because their aim is not conservative governance but confrontation and incitement of an anti-Washington base. For these folks the “best deal possible” is not a statement of mature leadership, but a sell-out.

Nevertheless, we also know that the cranky voices are a very small minority in the House (only 28 Republicans voted against the short-term CR in the wee hours of the night). Moreover, Tea Partyers whom the Democrats were setting up to take the fall in the event of a shutdown were overwhelmingly positive about the deal. Perhaps the anti-dealmaking right is largely a creation of liberal media and of a few sour conservative pundits.

The fact that the president is now racing to catch up with the spending cutters and that the right is more united than ever tells you how large the impact of the 2010 midterms is. And those on the left who oppose even the mildest form of fiscal discipline or who say, “Yeah, that’s the ticket — Obama was on board all along!”as well as those on the right who whine about any deal should not be taken seriously. After all, the CR shows how little credibility they have.