Rick Perry led the 2012 Republican Presidential race right around this time in 2011, and then flopped badly with his poor performance in a debate where he could not remember the third government agency he wanted to abolish. He came back this year, with nice new glasses, and claiming he had improved his ability to perform in debates, but the polls never showed he could recover from his famous disaster four years ago.
Scott Walker led the polls in Iowa and was seen earlier this year as a major contender for 2016, but he totally collapsed, despite having the backing of the Koch Brothers, and now, like Perry, was a total bomb in debates.
Their being the first two to leave the GOP race shows being ahead in the third year of a Presidential term is often the death knell, and it will be followed soon by the likes of Chris Christie, Bobby Jindal, Lindsey Graham, Rick Santorum, George Pataki, Jim Gilmore, Mike Huckabee, Ted Cruz and other pitiful candidates, including Dr. Benjamin Carson and Carly Fiorina, despite their being high in the polls at the moment, and Rand Paul.
At the end, it looks more than ever that the final four will be Donald Trump, Jeb Bush, Marco Rubio, and John Kasich.