I wish President Obama would avoid hypotheticals which Trump could grab upon to make claims. There is nothing like a claim that cannot be fact checked, where Trump does not shine.
Even though simple mathematics would justify Obama's remark, as to his electability for a third term if the law permitted, since Obama
who not only had a high approval rate among the electorate, would have easily garnered Hillary's votes which gave her a 2.8 million more votes than Trump obtained, plus those of voters who wavered because of her emails. A Trump claim to the contrary costs him nothing and can't be disproven to boot.