According to the constitution, there is no need to have a legal and criminal definition of incitement for the president to be impeached. There is no leniency due to legal definitions of causation..
Furthermore, the text of the impeachment is clear on what ideas and words he used to incite people.
The text of the impeachment is:
“On January 6, 2021, pursuant to the 12th Amendment to the Constitution of the United States, the Vice President of the United States, the House of Representatives, and the Senate met at the United States Capitol for a Joint Session of Congress to count the votes of the Electoral College. In the months preceding the Joint Session, President Trump repeatedly issued false statements asserting that the Presidential election results were the product of widespread fraud and should not be accepted by the American people or certified by State or Federal officials. Shortly before the Joint Session commenced, President Trump, addressed a crowd at the Ellipse in Washington, D.C. There, he reiterated false claims that “we won this election, and we won it by a landslide.”
“He also willfully made statements that, in context, encouraged – and FORSEEABLY (my emphasis) resulted in – LAWLESS (my emphasis) action at the Capitol, such as: “if you don’t fight like hell you’re not going to have a country any more.” Thus INCITED (my emphasis) by President Trump, members of the crowd he had addressed, in an attempt to, among other objectives, interfere with the Joint Session’s solemn constitutional duty to certify the results of the 2020 Presidential election, unlawfully breached and vandalized the Capitol, injured and killed law enforcement personnel, menaced Members of Congress, the Vice President, and Congressional personnel, and engaged in other violent, deadly, destructive and seditious acts. ”