This worthy idea actually orginated with Professor R. Lawrence Butler of Rowan University. On October 17, 2001, he wrote in The Hill:
The majority leader is the Senate's closest parallel to the Speaker of the House in that he is responsible for managing the Senate schedule and serves as the chief spokesperson and legislative tactician for his party caucus.
In a time of crisis, it is vital that our leaders have both the political legitimacy and the leadership ability needed to soothe an anxious public. All other posts in the line of succession have some claim to a broad electoral mandate. The entire House chooses the Speaker; Cabinet secretaries are appointed by a nationally elected president and confirmed by the entire Senate. The president pro tem's sole claim to the office is the willingness of the voters in a single state to keep sending him back to Washington decade after decade.
Would the sight of an aging senator taking the presidential oath of office be of particular comfort to a country rocked by the death of its three top political leaders? The times demand that we make a wiser choice.