Senate Chaplain Barry C. Black. (Drew Angerer/ASSOCIATED PRESS)

The Senate doesn’t do it on purpose, but it begins every day by acting out a drama in three parts and with the moral arc of a Shakespeare tragedy.

Act one is a prayer. Barry C. Black, the Senate’s chaplain, asks God for unity, wisdom and cooperation, pleading for the Senate in a voice as slow and solemn as a hearse.

Act two is the pledge. Lawmakers from both parties both pledge allegiance to the flag of one nation, indivisible.

Act three is the plot twist. After all the talk about unity and cooperation, the leaders of both parties stand up for their part of the morning ritual.

Which is denouncing one another as enemies of progress, abusers of the public trust, and raw sewage in the great river of American ideas.

“Do nothing, and protect the millionaires.” That was Sen. Richard J. Durbin (Ill.), the Senate’s number-two Democrat, one day this week. He was accusing Republicans of abandoning the middle class during the economic crisis.

“This whole thing is a charade.” That was Minority Leader Mitch McConnell (R-Ky.). He stood stood up after Durbin, to ridicule the Democratic plans for economic recovery. “I think the American people deserve better.”

The bitter turn of this daily ritual has been particularly notable this week, as the two parties returned to fighting after an ultra-brief experiment with cooperation. Both had pledged to find common ground on the issue of jobs. Then both remembered there was almost no common ground to find.

In his office, tucked away down a quiet Senate hallway, the Senate’s chaplain said he doesn’t take it personally — this week or any other — when his flock goes back to squabbling.

“I don’t take it as any kind of litmus test on the efficacy of my intercession,” Black said.

The Senate has begun its working sessions with prayer since 1789. It has never been an easy job preaching peace to a flock whose main job is to fight one another: Peter Marshall, chaplain in the 1940s, said he was the Senate’s equivalent of parsley — mainly there for decoration.

Black, who has the job today, is a Seventh-Day Adventist who rose to the rank of rear admiral as a Navy chaplain. His job now is bigger than giving the Senate’s morning prayer: He counsels senators privately and leads Bible studies for the Capitol’s cooks, cops and janitors.

But Black still takes the parsley role very seriously. He writes his opening prayers in a Capitol office with stunning views of the Mall’s monuments — reminders, for him, of how God has helped America through past crises.

“There’s something about this view that drives home to me the sovereignty of God, and the unstoppable nature of providence,” Black said in an interview. “Like the coming of morning, [it] will not be restrained.”

His prayers, generally, ask God to instill senators with virtues of good government. Often, there are nudges toward bipartisan cooperation — in a Congress that has seen very little of it so far.

“Lord, infuse them with a spirit of reconciliation,” Black prayed Sept. 13, “that will break down divisive walls, bringing harmony and cooperation.”

“Give them also a spirit of unity,” Black said the next day. “And the wisdom to have respect, one for the other.”

“Today, enable the members of this body to experience your presence, and to receive your wisdom,” Black said Wednesday. “May they receive these blessings — aware of your counsel that to whom much is given, much is required.”

But often, there are few senators in the chamber to hear him. And those that are there often don’t seem to have listened.

The proof of that usually comes in “Leader Remarks,” when the two parties’ bosses come out to utter the first complaints, accusations and deprecations of a long day. This tradition of tit-for-tat “Leader Remarks” dates to about 1986, when C-Span cameras began broadcasting from the Senate.

Up in that office overlooking the Mall, Black said — slowly, solemnly — that he never feels as though he failed when he hears the day’s debate turning bitter again.

“These statements that are usually being read,” he said, “have obviously been prepared before the prayer.”

On Thursday, the Senate’s prayer was done by a guest chaplain, Silvester S. Beaman of Bethel African Methodist Episcopal Church in Wilmington, Del. Beaman, like Black, also called on God to awaken the Senate’s better angels: “Use the collective resolve of our United States Senate as your instrument, bringing wholeness and peace.”

Then, right on schedule, the Senate demonstrated that wholeness and peace were not on its agenda.

Senate Majority Leader Harry M. Reid (D-Nev.) stood up to give a speech denouncing House Republicans for a budget bill that would cut more funds than Democrats want. It was “so wrong,” Reid said, and “very, very unfair.”

“We really are at an impasse here,” Reid said, talking about the bill. Continuing disagreements threatened to shut down the federal government at the end of the month. “Not just because of what we’re doing. But because of what they’re doing.”

As soon as he finished, McConnell was waiting to speak.