Tuesday’s Capitol Hill testimony by Gen. David Petraeus, commander in Iraq, and Ambassador Ryan Crocker has an air of unreality about it, for the hearings will have little to do with oversight of the executive branch, which is their ostensible purpose.

Let’s start with Sen. John Kerry’s (D-Mass.) comment, quoted by The Washington Post on Monday, that,

“It’s all completely predictable this time, what everyone is going to say.”

This is true. Democrats have long said the Iraq war is a failure and it is past time to pull out American troops. Republicans argue that the troop surge executed by Petraeus has succeeded and there is a real chance of America achieving a good proportion of its goals.

These positions have hardened as the November election has drawn nearer. Each party knows the position it is fighting from, and lawmakers from both sides can be expected to stick to their scripts. As is fairly common, the hearing will therefore be less about what executive branch officials say to lawmakers than about what lawmakers say to the public.

Thus, the hearing is (and is bound to be) almost entirely political. Which makes it odd for Sen. Joseph Biden (D-Del.), chairman of the Foreign Relations Committee, to say, “The biggest mistake we could make is politicizing this …” when in truth, there is no way he can stop it.

Certainly he cannot by declining, as he has, to allow Sen. Barack Obama (D-Ill.), front-runner for his party’s presidential nomination, to move up the pecking order to where he could be certain of speaking in time for the evening news.

Sen. John McCain (Ariz.), the Republican nominee-in-waiting, will take position front and center during the Armed Services Committee hearing because, as ranking member, he may cut in freely, and anyway speaks immediately after the chairman, Sen. Carl Levin (D-Mich.).

Sen. Hillary Rodham Clinton (D-N.Y.), another member of Armed Services and the third of the three plausible presidential nominees, will, meanwhile, be waiting her turn low down the seniority list.

Seniority often gives way to convenience in speaking order at hearings. Lawmakers get permission to go out of turn so they can rush away to another event on their schedule. It would be odd for the Democrats to keep their two candidates waiting, when all eyes are on them, although Biden (whose own presidential poll numbers never broke out of the margin of error) could be forgiven for asking of Obama, “Must he have everything?”

These are the first hearings in a long while that the presidential hopefuls have attended. With the events ineradicably political, the Democrats surely would want to help their candidates shine as brightly as McCain.