The Democratic Party hasn't chosen its candidate yet, but either way they're bound to lose.

Literal

Democratic-Party [topic-は] yet candidate [object-を] hasn't-decided but [concessive-が], whichever-way [topic-も] losing [inference-に決まっている].

Three things worth noticing. まだ...ていない is the standard 'not yet X' pattern — ~ている negated for incomplete actions. どっちにしても ('whichever way,' 'in any case') is a casual dismissive that resigns to both outcomes at once. And ~に決まっている literally says 'is settled at [losing],' a strong confident inference — 'bound to X,' 'there's no way not to X' — much stronger than simple だろう.