Which external factor is cited as a possible influence on hiring decisions outside of the candidate's control?

Internal politics or budget changes.

Hiring decisions are complex processes influenced by numerous variables that have nothing to do with a candidate's qualifications or performance during the interview. The text explicitly lists several such external factors that can sway the outcome, even after a candidate performs well. These uncontrollable elements include shifts in internal organizational politics, unexpected budget adjustments leading to hiring freezes or role modifications, or the sudden prioritization of another candidate who possesses a single, highly specific, niche skill that became critical to the team at the final moment. Recognizing these external drivers helps in de-personalizing the setback.