Elite and mass level politics is increasingly characterised by the expression of strong
feelings towards both partisan and issue-based out-groups. But are these expressions mostly
symbolic in nature or can they be used by campaigns to activate supporters to take costly
political action? We test if fundraising emails containing negative or positive political cues
lead supporters of a party to take costly action via a large randomized field experiment
conducted in collaboration with a UK political party. We expose supporters of a party
to negative or positive political identity cues and identify the effect of these cues on time-stamped
donation behaviour. We find that emails containing negative as opposed to positive
identity cues lead to a higher number and frequency of donations. However, the overall
donation amount remains unchanged. The type of identity invoked, partisan or issue-based,
does not condition the effect of negative identity cues. Our results provide novel experimental
evidence of how expressive negative political identities materialize in real-world campaigns.