Learn Russian: Даже если кампания будет трудной, любой активист готов помочь. - Even if the campaign is difficult, any activist is ready to help.

In English, we often use the present tense after 'if' or 'even if' to talk about the future (like 'Even if it is difficult tomorrow'). Russian is more strictly logical: if the event is in the future, you must use the future tense. Because this difficulty is seen as a real possibility rather than a purely hypothetical one, we use the indicative будет rather than the subjunctive была бы.

Could I use the subjunctive mood with даже если in this sentence?

Yes, but it changes the meaning. If you said Даже если бы кампания была трудной (Even if the campaign were difficult), it would mean you consider the difficulty to be highly unlikely or purely theoretical. Using the indicative future будет means you think the campaign being difficult is a very real possibility.

Why is the adjective трудной in the instrumental case instead of the nominative?

When an adjective follows the future tense of the verb 'to be' (будет), it is very commonly put in the instrumental case. While the nominative is sometimes possible, the instrumental is the most natural and standard choice for native speakers to describe a future state or condition.

Why is любой used here for 'any' instead of какой-нибудь?