how can trump say it was a rigged election if he won?

Trump can say it because he appears to use “rigged” as a political talking point, not as a literal claim that the overall election result he won was fake. Reports show he has repeatedly called elections “rigged” even in contexts where he won or when he is trying to argue the system is unfair or biased against him.

Why that happens

• He often uses “rigged” broadly to mean the process was unfair, media coverage was hostile, rules were bad, or opponents cheated, even when there is no evidence that the result was actually stolen.

• In practice, he has also used the word to refer to elections he lost, especially the 2020 race, which he has repeatedly and falsely claimed was stolen.

• That means the phrase can be politically useful for him even when it sounds contradictory to everyone else.

The contradiction

If someone won an election, calling it rigged sounds inconsistent because a rigged election usually implies a manipulated outcome. But Trump’s rhetoric often treats “rigged” as a catch-all for any system he dislikes, not a strict factual statement about the final vote count.

What the reporting shows

Recent coverage says he has kept repeating claims that elections are “rigged” and “dishonest,” while experts and courts have found no evidence of widespread fraud in the 2020 election. Other reporting also notes that he has made these kinds of claims for years, including after elections he lost.

TL;DR: He can say it because it is part of his political narrative, even if it conflicts with the fact that he won that election; the word is being used more as a slogan than a precise description of events.