A lie is determined by intention.
If someone makes a claim knowing the claim is false, that is a lie. He intended to deceive, or lie, by intentionally stating an untruth.
If someone makes a claim he sincerely believed to be true, and it later turns out not to be true, that is not a lie. He did not intend to deceive and believed in the veracity of his claim, even if later events prove those claims wrong.
Most politicians speak untruths at some point, simply because they cannot always control legislative outcomes.
George H. W. Bush famously promised, “Read my lips, no new taxes.”