A possible defense is that the e-mail was dated May 13, 2017, five months after he left office, and therefore he was free to make such arrangements. There are two problems with that argument.
First, I hear earlier e-mails show discussions with individuals in China began much earlier, while Joe Biden was still vice president. They could reveal a serious conflict of interest at the least.
Second, the mere fact that Biden intended to make money by working with China after leaving the White House is an explosive campaign issue. For good reasons, the vast majority of Americans hold an unfavorable view of China and would likely punish a candidate who tried to go into business with the Communist government.
With the election clock ticking down, the stakes couldn’t be higher. Yet Biden failed the first test of how he will handle the scandal.