One Republican senator said Gingrich still has scars from his bruising battle with Democrats as Speaker in the 1990s. He is seen to suffer from the same problem some lawmakers think affects Trump: a short attention span.

Like Trump, Gingrich has a propensity for jumping onto grand ideas that are not so pragmatic, such as when he promised in 2012 to build a colony on the moon by 2020.

Christie learned about the intricate workings of the federal government as the former U.S. attorney for the district of New Jersey, a job that gave him oversight over various disputes between state interests and federal regulatory agencies.

But Christie hasn’t spent much time in Washington and doesn’t really know the players who would be crucial to passing Trump’s agenda. The businessman said in February, when he first started mulling potential running mates, that he wanted a political insider “because I want to get lots of great legislation.”

Some Republicans question Trump’s short-list and think he might be better off picking someone who can help him win a swing state like Ohio.