Retiring Rep. Adam Kinzinger (R-Ill.) said Friday that his "biggest regret" during his time in Congress was voting against the first impeachment of former President Trump.

Why it matters: Trump was impeached and later acquitted on two articles — abuse of power and obstruction of Congress — related to a phone call in which he pressed Ukrainian President Volodymyr Zelensky to investigate the Biden family. Trump's accusers alleged that he withheld much-needed military aid to force Zelensky's hand, which Kinzinger said has affected Ukraine's ability to defend itself against Russia.

What he's saying: "It’s important for political leaders to be transparent and admit regret when needed. The bottom line, Donald Trump withheld lethal aid to Ukraine so he could use it as leverage for his campaign," Kinzinger tweeted.