Haw. Rev. Stat. § 607
The credibility of a witness may be attacked by any party, including the party calling the witness.
HRS § 607
RULE 607 COMMENTARY
This rule, which is identical with Fed. R. Evid. 607, rejects the traditional theory that a party calling a witness "vouches" for his truthfulness and therefore is barred from impeaching him. See generally McCormick §38. As the Advisory Committee's Note to Fed. R. Evid. 607 puts it:
A party does not hold out his witnesses as worthy of belief, since he rarely has a free choice in selecting them. Denial of the right [to impeach] leaves the party at the mercy of the witness and the adversary.... The substantial inroads into the old rule made over the years by decisions, rules, and statutes are evidence of doubts as to its basic soundness and workability.
This rule supersedes a statute, Hawaii Rev. Stat. § 621-25 (1976) (repealed 1980) (originally enacted as L 1876, c 32, §58; am L 1972, c 104, §1(r)), which precluded a party from impeaching his own witness "by general evidence of bad character" but permitted impeachment by prior inconsistent statement when the witness "prove[d] adverse." In construing the provisions of the prior statute, the Hawaii courts suggested that a witness would "prove adverse" if his testimony was materially inconsistent with the prior statement, his inconsistency came as a surprise to the party offering his testimony, and he either expressly denied or, by evasion, implied a denial of the prior statement, Territory v. Witt, 27 H. 177 (1923); see also Kwong Lee Wai v. Ching Shai, 11 H. 444 (1898). Rule 607 thus effects a significant change in Hawaii law in accord with a growing trend in other jurisdictions, e.g., Cal. Evid. Code §785. Another good reason for abandoning the old impeachment limitation is that, as applied to defense witnesses, its constitutionality is suspect in criminal cases, see Chambers v. Mississippi, 410 U.S. 284 (1973).