During a campaign rally in Mosinee, Wisconsin, Trump accused Biden of softening on some promises he had made earlier in his campaign.
O'Rourke, who also ran for president in this election cycle, said during a December Democratic debate, "Hell, yes, we're going to take your AR-15, your AK-47.".
Biden "put Beto in charge of guns," Trump said Thursday.
In August, President Trump said that Biden would "hurt the Bible.
In August, the Democrat said that his belief system "teaches me to welcome the stranger, while President Trump tears families apart.".
After Sanders said his energy plan involved ending fracking with "no ifs, buts and maybes about it," Biden said he was also in support of that idea.
In an interview in May with CNBC, Biden said he would "not stop fracking."