If no candidate wins at least 270 electoral votes, the election of the President and Vice President moves to
This is called a contingent election. The elections of 1800 and 1824 were decided in this way.
Common Interpretation: Article II, Section 1, Clauses 2 and 3
From the National Constitution Center, Interactive Constitution
"Contingent Election of the President and Vice President by Congress: Perspectives and Contemporary Analysis"
From the Congressional Research Service (2016)
Electoral College & Indecisive Elections
"Presidents Must Be Elected Popularly: Examining Proposals and Identying the Natural Endpoint of Electoral College Reform"
From the Fordham University School of Law: Democracy and Constitution Clinic (2020)