WASHINGTON -

Republican Sen. Marco Rubio of Florida is planning a swing-state summer bus tour that will also roll through South Carolina, the early presidential primary battleground.

The bus tour, set for the week of the Fourth of July holiday, is aimed at promoting Rubio's autobiography, "An American Son."

Officially, Rubio's tour is aimed at selling books, but the freshman senator and possible vice presidential pick is set to make multiple stops -- not just in his home state of Florida but also in North Carolina and Virginia, critical presidential battlegrounds this fall.

On the way, he'll make several appearances in South Carolina, where Republicans hold their first-in-the-South presidential primary.

Rubio has been informally auditioning for the traditional vice presidential role as attack dog, leveling biting criticism at Democratic President Barack Obama.