(17.03.2020)
The nonpartisan Congressional Research Service reached the same conclusion when it investigated the question in the aftermath of 9/11.
Under the U.S. Constitution, Trump and Vice President Mike Pence cannot stay in office past their four-year terms without being reelected. If the election does not happen for any reason, constitutional rules of succession kick in.
That could mean a lawmaker down the line of succession who is not up for reelection could be the new president.