Harris will certainly take credit but recent asylum ban by Biden dropped numbers to their lowest since 2020.... quiets the argument Dems dont want to close the border or take tough action... each side can claim they took action on immigration so just becomes who lies better about it https://www.theguardian.com/us-news/article/2024/aug/09/migrant-crossings-biden-asylum-ban
Given deportations were higher under Clinton Bush and Obama it looks like Trump simply relied on what his predecessors were doing.... but if you sleep better think trump invented it go for it!
Trump tried to build a wall (which Clinton Bush and Obama did not) and the Democrats fought him at every turn.