Washington ? Congress called BP and its drilling partners to account Tuesday for a “cascade of failures” behind the spreading Gulf oil spill, zeroing in on a crucial chain of events at the deep-sea wellhead just before an explosion consumed the rig and set off the catastrophic rupture.

In back-to-back Senate inquiries, lawmakers chastised executives of the three companies at the heart of the massive spill over attempts to shift the blame to each other. And they were asked to explain why better preparations had not been made to head off the accident.

“Let me be really clear,” Lamar McKay, chairman of BP America, told the hearing. “Liability, blame, fault — put it over here.” He said: “Our obligation is to deal with the spill, clean it up and make sure the impacts of that spill are compensated, and we’re going to do that.”

Demonstrators stand with a 50-foot banner in front of the White House in Washington on Tuesday. The 50-foot banner was signed by Gulf residents and marched from the Department of Interior to the White House. The banner is to protest drilling of fossil fuels and reads “Obama: This is your crude awakening.”

By “over here,” McKay meant the witness table at which BP, Transocean and Halliburton executives sat shoulder to shoulder. And despite his acknowledgment of responsibility, each company defended its own operations and raised questions about its partners in the project gone awry.

Lawmakers compared the calamity to some of history’s most notorious mishaps from sea to space in the first congressional inquiry into the April 20 explosion and so-far unstoppable spill. In the crowded hearing room, eight young activists sat in quiet protest, with black T-shirts saying, “Energy Shouldn’t Cost Lives.” Several wore black painted spots near their eyes to symbolize tear drops made from oil.

Said Sen. Jeff Bingaman, D-N.M., chairman of the Energy and Natural Resources Committee, “If this is like other catastrophic failures of technological systems in modern history, whether it was the sinking of the Titanic, Three Mile Island, or the loss of the Challenger, we will likely discover that there was a cascade of failures and technical and human and regulatory errors.”

The corporate finger pointing prompted an admonishment from Republican Sen. Lisa Murkowski of oil-rich Alaska that “we are all in this together” in trying to shut off the oil and find a safer way to exploit vital energy.

“This accident has reminded us of a cold reality, that the production of energy will never be without risk or environmental consequence,” she said. Still, she said, “there will be no excuse” if operators are found to have violated the law.

Failure to cap the leak was intensifying impatience, from the contaminated Gulf waters to the White House.

“The president is frustrated with everything, the president is frustrated with everybody, in the sense that we still have an oil leak,” spokesman Robert Gibbs said. “That includes us, that includes everybody that’s involved with this.”

After an icelike buildup thwarted a plan over the weekend to siphon off most of the leak using a huge, 100-ton containment box, a second, smaller box was lowered into the water late Tuesday near the blown-out well. The box was being slowly submerged to the seabed but it won’t be placed over the spewing well right away. BP spokesman Bill Salvin said engineers want to make sure everything is configured correctly and avoid an ice buildup.

Salvin said undersea robots will position the box over the gusher by Thursday.

Ramifications from the environmental crisis spilled over into landmark climate change and energy legislation that is coming out today. The bill from Sens. John Kerry and Joe Lieberman proposes letting coastal states veto drilling projects off the shores of neighboring states if they can show the potential for harm.

The impact is being felt in the realm of regulation, too. Interior Secretary Ken Salazar proposed splitting his department’s Minerals Management Service in two to make safety enforcement independent of the service’s other main function: collecting billions in royalties from the drilling industry.