Would you please read the following sentence from a military letter to a state senator and correct it as pertains to using the word remain or remains? Your prompt reply would be greatly appreciated for this letter needs to be mailed ASAP. Thank you.

"Until there is a closing date for this campaign, the distribution of this medal to those who participated on Operation ENDURING FREEDOM, or who still remains in support of the campaign, has not been authorized."
I'd go with remain, plural use.
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those = who

so use the plural form of verb ' remain 'Emotion: smile
those who participated and remain, obviously. It's plural, right?