As the marathon meeting between rail industry and union representatives neared its 12th hour, the moment Biden administration officials viewed as equal parts inevitable and essential was set into motion.

It was time for President Joe Biden to call in and underscore the stakes. Biden's message was consistent with the one he'd delivered in private calls over the course of the last several weeks, sources said, but an urgency framed around just how devastating a rail shutdown would be for the country was palpable.

It would be another eight hours before the White House hit send on the President's statement announcing the tentative agreement, but Biden's call at a critical moment was emblematic of an approach as carefully calibrated as it was high stakes.

"Failure wasn't an option here," one source with direct knowledge of the call said. "Everyone knew the stakes, but the President really hammered home how deep and catastrophic leaving without an agreement would be for the entire country."