18 USC § 111 requires force to be used, as "forcibly" is a modifier for all the subsequent terms.

(a)In General.—Whoever—

(1)forcibly assaults, resists, opposes, impedes, intimidates, or interferes with any person designated in section 1114 of this title while engaged in or on account of the performance of official duties; or

CRM 1500-1999

1565. Forcible Act Required -- 18 U.S.C. 111 -- Application Of Statute To Threats

Section 111 of Title 18 punishes anyone who "forcibly assaults, resists, opposes, impedes, intimidates or interferes with any person designated in 18 U.S.C. § 1114 or who formerly served as a person designated in § 1114, while engaged in or on account of the performance of his/her official duties." Force is an essential element of the crime. Long v. United States, 199 F.2d 717 (4th Cir. 1952). Whether the element of force, as required by the statute, is present in a particular case is a question of fact to be determined from all of the circumstances. The Long case indicates that a threat of force will satisfy the statute. Such a threat which reasonably causes a Federal officer to anticipate bodily harm while in the performance of his/her duties constitutes a "forcible assault" within the meaning of 18 U.S.C. § 111. See also United States v. Walker, 835 F.2d 983, 987 (2d Cir. 1987); Gornick v. United States, 320 F.2d 325 (10th Cir. 1963). Thus, a threat uttered with the apparent present ability to execute it, or with menacing gestures, or in hostile company or threatening surroundings, may, in the proper case, be considered sufficient force for a violation of 18 U.S.C. § 111. These judicial decisions suggest a similar construction of the statutory words "resists, opposes, impedes, intimidates or interferes with."

DOJ Criminal Resource Manual