Throwing a liquid at someone is considered assault if I’m not mistaken.”
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In most jurisdictions it is an actual “battery.” In both cases it is still a misdemeanor unless (for instance if the actor was a conservative) it can be ramped up by other demonstrable circumstances.
52 U.S. Code § 20511 - Criminal penalties
A person, including an election official, who in any election for Federal office—
(1) knowingly and willfully intimidates, threatens, or coerces, or attempts to intimidate, threaten, or coerce, any person for—
(A) registering to vote, or voting, or attempting to register or vote;
(B) urging or aiding any person to register to vote, to vote, or to attempt to register or vote; or...
...shall be fined in accordance with title 18 (which fines shall be paid into the general fund of the Treasury, miscellaneous receipts (pursuant to section 3302 of title 31), notwithstanding any other law), or imprisoned not more than 5 years, or both.
The statute is specific that it's "any person" (singular). Arguably, the attacker could be charged for every individual at the event who was not already registered to vote.
52 U.S. Code § 10307 - Prohibited acts
No person, whether acting under color of law or otherwise, shall intimidate, threaten, or coerce, or attempt to intimidate, threaten, or coerce any person for voting or attempting to vote, or intimidate, threaten, or coerce, or attempt to intimidate, threaten, or coerce any person for urging or aiding any person to vote or attempt to vote, or intimidate, threaten, or coerce any person for exercising any powers or duties under section 10302(a), 10305, 10306, or 10308(e) of this title or section 1973d or 1973g of title 42.[1]