Protection from Evil cast on a player who's already under a Charm Person spell?

Question

I'm currently playing a D&D 3.5 campaign and in our last session our fighter has fallen under a Charm Person spell cast by an evil enemy spellcaster. My character is a Cleric and has access to both Protection from Evil and Magic Circle against Evil. If I cast the former upon the figher, or the other one so that the fighter is included in the affected area, what happens? I'm not sure how to interpret the spell's description. From the PHB (emphasis mine):

The barrier blocks any attempt to possess the warded creature (by a magic jar attack, for example) or to exercise mental control over the creature (including enchantment (charm) effects and enchantment (compulsion) effects that grant the caster ongoing control over the subject, such as dominate person). The protection does not prevent such effects from targeting the protected creature, but it suppresses the effect for the duration of the protection from evil effect.

Therefore, it seems that once the spell is cast the target becomes immune to the mental influence of the evil entity. However, the spell description also says that (emphasis mine)

If the protection from evil effect ends before the effect granting mental control does, the would-be controller would then be able to mentally command the controlled creature. Likewise, the barrier keeps out a possessing life force but does not expel one if it is in place before the spell is cast.

It is clear that the spell does not nullify Charm Person, but the controller seems (at least) to be unable to give orders to the targeted creature. What about the order given before Protection from Evil is cast? There are three possible interpretations:

1. Nothing happens, as the target was already Charmed before;
2. The creature is still Charmed but the evil guy cannot give new orders (as Protection suppresses the effects of Charm);
3. Charm Person is stopped for the duration of the Protection spell, and my fighter is free to act as he pleases.

Thank you for your input!

Answer 1

Protection from Evil suppresses the Charm Person effect for the duration of Protection (as Charm Person has the "Enchantment(Charm)" descriptor).

This suppression means the effect of Charm Person causing the target to view the caster's action in a positive light is removed, and the target behaves as they normally would. I would still rule that Charm Person can be broken by the caster threatening the target, even if Protection from Evil is suppressing the effect.

The secondary wording you bring indicates that if Protection from Evil ends before whatever effect causing the mental control/possession ends, then the control is re-instated. And notably in the case of possession/life-force sort of swapping effects, its not expelled, but made dormant.

So consider the following series of events:

1. Evil caster casts Charm Person on Fighter (who fails their will save), and tells them "Hey buddy, there is poison inside all of your allies' potion flasks, you should pour all of them out!." The spellcaster is 10th level, so the effect lasts for 10 hours.
2. Fighter fails the opposed Charisma check against the given order and goes about doing this thing. Note they still see their allies as allies, so the fighter isn't going to attack them, just try to "help" them (at worst this might mean rifling through their stuff at night, but almost certainly won't mean attacking their fellow party members).
3. Allied spellcaster sees the Fighter doing the outright stupid thing and casts Protection from Evil on them. The allied spellcaster is level 9, so Protection from Evil is 9 minutes in duration.
4. For that duration, the Fighter has the Charm suppressed. They are no longer magically compelled to think highly of the Evil spellcaster, and probably think its a bad idea to destroy potions on the dubious word of some black-robed individual they just met (what you're actually hitting here is a conversation regarding player agency, and why hitting players with Charm Person is often considered unwise and in bad-form; because it is tricky, and Charm Person doesn't magically allow you to control someone, just seriously influence they feel about something). Given that the target no longer is compelled to think in any particular way, the controlling player is free to say what their character does.
5. At the end of the duration, Charm Person re-instates itself and the Fighter once again thinks of the Evil Caster as their buddy. Note that the "order" given with Charm Person isn't magically empowered, just the result of a very good friend being very convincing in telling the target what to do. With that, I don't think the Fighter would go about destroying potions again, as their normal self did re-assert during the duration of Protection from Evil, and they were able to freely consider it as a bad idea.

Answer 2

Charm Person is suppressed while the Protection From Evil spell persists.

To requote Protection from Evil

The barrier blocks any attempt to possess the warded creature (by a magic jar attack, for example) or to exercise mental control over the creature (including enchantment (charm) effects and enchantment (compulsion) effects that grant the caster ongoing control over the subject, such as dominate person). The protection does not prevent such effects from targeting the protected creature, but it suppresses the effect for the duration of the protection from evil effect.

Lets look at Charm Person

Charm Person

Enchantment (Charm) [Mind-Affecting]

This charm makes a humanoid creature regard you as its trusted friend and ally (treat the target’s attitude as friendly). If the creature is currently being threatened or attacked by you or your allies, however, it receives a +5 bonus on its saving throw.

The spell does not enable you to control the charmed person as if it were an automaton, but it perceives your words and actions in the most favorable way. You can try to give the subject orders, but you must win an opposed Charisma check to convince it to do anything it wouldn’t ordinarily do. (Retries are not allowed.) An affected creature never obeys suicidal or obviously harmful orders, but it might be convinced that something very dangerous is worth doing. Any act by you or your apparent allies that threatens the charmed person breaks the spell. You must speak the person’s language to communicate your commands, or else be good at pantomiming.

Right in the first portion of Charm Person, we can see that it's a (Charm) effect and is [Mind Affecting]. While it doesn't allow you to give commands telepathically like Dominate Person does, that doesn't mean that it isn't allowing you mental control of the target, which is clearly evidenced by the fact that the spell has the [Mind-Affecting] tag.

When they say "mental control" they don't mean you controlling them with your mind, them mean you controlling their mind, which is specifically what (Charm) and [Mind-Affecting] spells do.

Since Charm Person is not a possession effect, Protection From Evil does not prevent it from taking hold, but since it is a (Charm) effect that allows mental influence over the target (it allows you to give the target orders and compel them to obey), Protection From Evil will suppress that Spell while it's active.

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For reference:

The Enchantment (Charm) and Enchantment (Compulsion) subschool descriptions:

Charm
A charm spell changes how the subject views you, typically making it see you as a good friend.

Compulsion
A compulsion spell forces the subject to act in some manner or changes the way her mind works. Some compulsion spells determine the subject’s actions or the effects on the subject, some compulsion spells allow you to determine the subject’s actions when you cast the spell, and others give you ongoing control over the subject.