Julian Zelizer is a professor of history and public affairs at Princeton University and author, with Kevin Kruse, of the new book "Fault Lines: A History of the United States Since 1974." Follow him on Twitter at @julianzelizer. The opinions expressed in this commentary are his own. View more opinion at CNN.

(CNN) If the economy falls apart, it's hard to see how President Trump wins reelection.

With the stock market in a state of uncertainty and the possibility of a global recession becoming very real, Republicans are worried.

A recession is what could keep Trump off the list of two-term presidents and relegate him to the one inhabited by Herbert Hoover, Jimmy Carter and George H.W Bush.

Trump realizes the danger: on Thursday, he tweeted that the media is "doing everything they can to crash the economy because they think that will be bad for me and my re-election. The problem they have is that the economy is way too strong and we will soon be winning big on Trade, and everyone knows that, including China!"

A good economy is not enough to guarantee the President reelection, given that voters are registering concern about other issues, such as his conduct in office and gun control -- but a very bad economy is more than he could withstand.

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