Bernie Sanders' momentum is spreading as the senator addressed the biggest crowd of Iowa so far this election cycle.

The Vermont presidential candidate drew more than 2,500 people in Council Bluff, Iowa, on Friday night, the largest crowd for a presidential candidate in the first-in-the-nation caucus state, the Washington Post reported.

A few days after more than 10,000 people showed up to a rally in Wisconsin, the Post reported.

The independent senator has been drawing fervent interest on the campaign trail with rhetoric on income inequality and the influence of the "billionaire class" in politics, according to the Post.

Despite the huge crowds, Hillary Clinton holds a formidable lead in Iowa. Clinton garners about 54 percent of the vote to Sanders' 20 percent, according to the latest RealClearPolitics average of polling data.

Things are more heated in New Hampshire, with Clinton holding about a 15-point lead in the primary, according to RealClearPolitics.

Sanders has emerged, however, as the leading threat to Clinton for the Democratic nomination, with candidates Jim Webb, Martin O'Malley and Lincoln Chafee all polling in the low single digits in Iowa and New Hampshire, RealClear's data shows.