Donald Trump lengthened his lead in the Republican contest by winning most states on offer.
In the Oxford dictionary, the phrase "on offer" has two meanings:1. that can be bought, used, etc. 2. on sale at a lower price than normal for a short period of time. Neither of them, in my opinion, makes any sense in the sentence above, an excerpt from the Economist (March 5, 2016). How could Donald Trump buy or "use" those states? I am confused.
Could someone please paraphrase the sentence? Thank you.