Sen. Tom Cotton on Monday slammed Sen. Cory Booker for planning to testify against the attorney general nomination of fellow Sen. Jeff Sessions, accusing the New Jersey Democrat of a "disgraceful breach of custom" designed to boost his 2020 presidential ambitions.Cotton (R-Ark.) leveled his charges hours before Booker is set to appear alongside other Congressional Black Caucus members during the second day of Sessions' confirmation hearing.