Learn Spanish (Latin America): No podemos dejar que nos traicionen ahora.

The verb dejar (to let or allow) is a verb of influence. When you allow someone else to do something, there is a change of subject from the main clause (we allow) to the dependent clause (they betray). This triggers the use of que followed by the subjunctive.

Why does nos go before traicionen instead of attaching to dejar?

The pronoun nos is the direct object of traicionar (they are betraying us). Because traicionen is a conjugated verb in a new clause, the pronoun must go right in front of it. If you attached it to dejar (as in dejarnos), it would mean 'We cannot let ourselves', completely changing the meaning.

Is it possible to use the infinitive instead, like dejarlos traicionarnos?

Technically, dejar is one of the few verbs of influence that can take an infinitive even with a subject change (like déjame ir). However, piling up attached pronouns on two different infinitives sounds incredibly clunky. Using dejar que with the subjunctive is much more natural and preferred here.

How does this sentence fit into a lesson on warnings and threats?

Even though it doesn't use the specific como + subjunctive structure taught in this lesson (such as Como nos traicionen, verán), sentences expressing what you will or will not allow often serve as the dramatic context for a threat. It also provides excellent practice for another essential B1/B2 subjunctive trigger: verbs of influence.