Democratic presidential nominee Joe Biden has cemented his national lead over President Donald Trump a month ahead of Election Day with a 16-point lead.

A CNN poll published Tuesday of likely voters showed 57% preferring Biden to Trump’s 41%. The previous version of the poll, conducted in late August among registered voters, showed Biden with an 8-point lead, ahead of Trump 51-43%.

The latest poll surveyed likely voters Thursday through Sunday, after the first presidential debate and largely after Trump’s announcement on Friday that he had contracted COVID-19.

While Biden has opened a large national lead, electoral analysts encourage people to give more weight to swing-state polls — in order to avoid a repeat of 2016, where former Democratic nominee Hillary Clinton polled better nationally, won the popular vote and lost the election.

RealClearPolitics average of polling in top battleground states shows Biden up in every state, but by a much slimmer margin (4.6 points on average), ranging from a 1.4-point lead in North Carolina to 7.1 points in Pennsylvania.

The national CNN poll, conducted by SSRS, surveyed 1,001 likely voters from Oct.1-4 and has a margin of error of +/-3.6%.