West Virginia University athletic officials spent most of Tuesday preparing to leave the Big East Conference for the Big 12. The Mountaineers’ athletic director, Oliver Luck, was so sure of the move that he tipped off Big East colleagues Monday night and told staff members Tuesday.

But everything changed Tuesday evening, as the Big 12 backed off its assurances to West Virginia. Hard lobbying from another candidate from the Big East, Louisville, has created a heated race for the remaining slot in the Big 12 that Missouri is expected to vacate soon. (Missouri is still headed to the Southeastern Conference after it sorts through its exit issues with the Big 12.)

A person with direct knowledge of the situation said it was “too close to call” between West Virginia and Louisville.

Two other people with direct knowledge said that the lobbying of the Senate minority leader, Mitch McConnell, Republican of Kentucky, had helped Louisville. His communication with Oklahoma’s president, David Boren, a former senator, and Texas Tech’s chancellor, Kent Hance, a former congressman, played a role in raising Louisville’s fortunes. Hance confirmed that McConnell called him to push Louisville.