https://www2.law.temple.edu/voices/taking-the-sting-out-using-direct-examination-to-anticipate-and-undercut-attacks-on-your-witness/
But this is wrong in two regards – the limitation is actually as to bolstering with character for truthfulness, which may occur only after an averment of the witness having an untruthful character; and it is inapposite when the form of bolstering has the appearance of attacking one’s own witness.