Four of the debates will be held in early nominating states.
The former governor launched his presidential bid from his hometown of Hope, Ark.
Bush calls his relationship with Mexico "very profound."
The Ohio governor will tape a TV appearance and meet with local leaders.
Club for Growth is spending $100,000 on an ad that will run in Iowa and South Carolina.
Her unfavorable ratings are up 6 percentage points, but she still tops Republicans.
Walker polls high among hopefuls, though he has yet to officially declare.
"People like to hear me speak,” Clinton said.
Fiorina launched her bid with attacks on Hillary Clinton.