Many political statements include statistics and I generally like to see if there is any truth to those statistics. While the truthfulness of the statement as a whole could be pretty subjective, I think most statistics can be analyzed objectively. Is it considered on-topic to ask about specific statistics used in political statements?
If you want to know where they got their statistics from, I'd certainly consider that on topic. An answer to that question would help you make sense of what a politician is saying and what their positions are.
Be careful though, If you know where a politician is getting their statistics from, but you want to otherwise fact check their source, then you might find yourself in a situation where you have numerous other sources either affirming or debunking those statistics, and it is very possible for that question to be too broad
When you want to fact-check a statement made by a politician, then this is a better question for the website Skeptics Stackexchange. It specializes on verifying claims by notable people or organizations.