We study the communication strategies on Twitter-X of 367 political leaders in 21 countries, focusing on electoral competition between populists and non-populists. We measure polarization by the ease with which the leader can be classified as populist or not, conditional on his tweet. We find that political rhetoric becomes more polarized before and around elections dates. This happens because, in pre-electoral quarters, opposite leaders are more likely to: i) talk about different topics, and ii) frame differently the same issues. Our results are consistent with competing politicians targeting different voters, rather than appealing to the same swing voters.