Dogged by delays and intense pressure from the Obama administration, BP Plc faces a pivotal day on Wednesday as it attempts a tricky plan to clog the gushing Gulf of Mexico oil well five weeks into the disaster.

If the “top kill” procedure joins the list of BP failures to plug the leak, U.S. President Barack Obama’s government may have no choice but to take central charge of the response to what is considered the worst oil spill in U.S. history.

Obama has told aides in recent days to “plug the damn hole” and he will head to the Louisiana Gulf coast on Friday for the second time since the April 20 rig blast that killed 11 and unleashed the oil.