No evidence

“The president retweeted assertions that Romney “stabbed Trump in the back” by joining Democrats in attempts to overturn the 2016 election, and that the Utah senator was connected to unsubstantiated claims that Hunter Biden, the son of former Vice President Joe Biden, was corruptly involved with the Burisma Holdings energy company in Ukraine.”Feb. 9, 2020

“…Hunter Biden, the son of former Vice President Joe Biden, was corruptly involved with the Burisma Holdings energy company in Ukraine.”