Republican senator Ted Cruz tried to give a lesson in politics to a Harvard professor in an angry exchange sparked by the Trump Administration’s decision to pull out of the Paris climate deal.

Cruz, of Texas, rebuked the notion that the United States was created through an international agreement, not the Declaration of Independence, after Joyce E. Chaplin, the chair of American Studies and history professor at Harvard University, shared her take on the U.S. withdrawal from the global agreement to fight climate change.

The USA, created by int’l community in Treaty of Paris in 1783, betrays int’l community by withdrawing from #parisclimateagreement today — Joyce E. Chaplin (@JoyceChaplin1) June 1, 2017

Just sad. Tenured chair at Harvard, doesn’t seem to know how USA was created. Not a treaty. Declaration+Revolutionary War+Constitution=USA. https://t.co/tQALvjdkTs — Ted Cruz (@tedcruz) June 2, 2017

Chaplin said the United States was betraying the international community that established it by not abiding by the climate accords, citing the agreement that ended the Revolutionary War. The Treaty of Paris was signed by the U.S., Britain, France, Spain, and the Dutch Republic in 1783. In addition to stopping the conflict, it was an agreement to recognize territory claims made by each signatory.

Sad. US Senator, Harvard Law degree. Doesn’t know that national statehood requires international recognition. https://t.co/gcxtJifWCl — Joyce E. Chaplin (@JoyceChaplin1) June 2, 2017

Lefty academics @ my alma mater think USA was “created by int’l community.” No–USA created by force, the blood of patriots & We the People. https://t.co/zOxVdj21en — Ted Cruz (@tedcruz) June 2, 2017

Senator Cruz sparked the debate by saying Chaplin didn’t understand how the United States came to be, prompting a reminder from the Harvard professor that statehood requires international recognition. Cruz, himself a Harvard alum, replied by dismissing the historian as one of the “lefty academics” from his alma mater.