The Republican field

Republican presidential candidate and former Texas Governor Rick Perry formally announces his candidacy for the 2016 Republican nomination for president at an event in Addison, Texas, June 4, 2015. REUTERS/Mike Stone

Senator Marco Rubio autographs a magazine with his picture on the cover after he announced his bid for the Republican nomination in the 2016 U.S. presidential election race during a speech at Freedom Tower in Miami, April 13, 2015. REUTERS/Carlo Allegri

Senator Lindsey Graham holds three month-old Elia Lionhood during a campaign stop at MaryAnn's Diner in Derry, New Hampshire, June 2, 2015. REUTERS/Brian Snyder

Senator Ted Cruz stands on stage with his wife Heidi and their daughters Catherine and Caroline, after he confirmed his candidacy for president during a speech at Liberty College in Lynchburg, Virginia, March 23, 2015. REUTERS/Chris Keane

Senator Rand Paul speaks to supporters during a campaign event at the National Society for Hebrew Day Schools in the Brooklyn borough of New York April 27, 2015. REUTERS/Brendan McDermid

Carly Fiorina waits at her reception to greet her next attendee at the Republican Party of Iowa's Lincoln Dinner in Des Moines, Iowa, May 16, 2015. REUTERS/Jim Young

Jeb Bush waves as he departs after speaking to the Greater Salem Chamber of Commerce in Salem, New Hampshire, May 21, 2015. REUTERS/Brian Snyder

Rick Santorum is flanked by his daughter Elizabeth and wife Karen as he formally declares his candidacy for the 2016 Republican presidential nomination during an event in Cabot, Pennsylvania, May 27, 2015. REUTERS/Aaron Josefczyk

Supporters of Ben Carson prepare their booth at the Southern Republican Leadership Conference in Oklahoma City, May 21, 2015. REUTERS/Rick Wilking

Former New York Governor George Pataki greets supporters after formally announcing his candidacy for the 2016 Republican presidential nomination in Exeter, New Hampshire, May 28, 2015. REUTERS

Louisiana Governor Bobby Jindal speaks at the Southern Republican Leadership Conference in Oklahoma City, May 22, 2015. REUTERS/Rick Wilking

Retired neurosurgeon Ben Carson stands with his wife Candy as he officially launches his bid for the Republican presidential nomination in Detroit, May 4, 2015. REUTERS/Rebecca Cook

Wisconsin Governor Scott Walker poses with former governors Jim Gilmore of Virginia (C) and Bob Ehrlich of Maryland (L) for a photo during a sunset cruise with the Belknap County Republicans in Laconia, New Hampshire, May 29, 2015. REUTERS/Dominick Reuter

Former New York Governor George Pataki greets supporters after formally announcing his candidacy for the 2016 Republican presidential nomination in Exeter, New Hampshire, May 28, 2015. REUTERS/Domin

Jeb Bush takes questions at a town hall meeting in Reno, Nevada, May 13, 2015. REUTERS/James Glover II

Senator Ted Cruz waves to the crowd after speaking during the Freedom Summit in Greenville, South Carolina, May 9, 2015. REUTERS/Chris Keane

Republican party paraphernalia vendor Kelly Steele displays a pair of campaign eyeglasses for Marco Rubio prior to Rubio's formal declaration of his bid for the Republican nomination in the 2016 U.S. presidential election race, at the Freedom Tower in Miami, April 13, 2015. REUTERS/Carlo Allegri

Jeb Bush poses for a selfie during a town hall meeting in San Juan, April 28, 2015. REUTERS/Alvin Baez

An audience member waves bumper stickers that read "Stop Hillary" at the First in the Nation Republican Leadership Conference in Nashua, New Hampshire, April 18, 2015. REUTERS/Brian Snyder

A ring worn by former Republican Governor of Texas Rick Perry is seen as he points during his speech at the Freedom Summit in Greenville, South Carolina, May 9, 2015. REUTERS/Chris Keane

Protestors against Senator Marco Rubio gather outside the Freedom Tower prior to Rubio's formal declaration of his bid for the Republican nomination in the 2016 U.S. presidential election race, in Miami, April 13, 2015. REUTERS/Carlo Allegri

A supporter of Marco Rubio is pictured prior to Rubio's formal declaration of his bid for the Republican nomination in the 2016 presidential election race, at the Freedom Tower in Miami, April 13, 2015. REUTERS

Governor of Wisconsin Scott Walker waits backstage before speaking at the Republican Party of Iowa's Lincoln Dinner in Des Moines, Iowa, May 16, 2015. REUTERS/Jim Young

Carly Fiorina speaks during the Freedom Summit in Greenville, South Carolina May 9, 2015. REUTERS/Chris Keane

Ben Carson talks to pastors and community leaders during a meeting at the Bilingual Church in Baltimore, Maryland May 7, 2015. REUTERS/Carlos Barria

Rick Santorum reacts as he holds Wyatt Owen, 9 months, during a campaign stop at the Food Truck Bash in Travelers Rest, South Carolina May 31, 2015. REUTERS/Chris Keane

T-shirts supporting Marco Rubio are pictured for sale at the Freedom Tower in Miami April 13, 2015. REUTERS/Carlo Allegri