In the homestretch before Iowa votes on Monday, Bernie Sanders has overtaken Joe Biden as the 2020 Democratic candidate getting the most attention online, according to data from NewsWhip provided exclusively to Axios.

Why it matters: Biden had led for the 17 weeks prior, and the numbers show that at the most important moment of the primary to date, Sanders' profile is peaking, accompanied by climbing poll numbers.

Between the lines: For much of the primary, most positive sentiment around Biden online has been around stories that point to his ability to beat Trump.

Sanders supporters are looking to make the same case. In January, the biggest single story around him wasn't the dustup with Elizabeth Warren or being slammed by Hillary Clinton, but a Newsweek writeup of a poll showing that Sanders leads Trump by the biggest margin of all Democratic candidates.

By the numbers: Stories about Sanders have generated more interactions on social media (likes, comments, shares) than stories about Biden over each of the last three weeks, totaling 20.1 million interactions to Biden's 14.2 million.

When Biden held the top spot, part of his lead could be attributed to his role in the saga that led to Trump's impeachment.

During that period, Sanders has eaten into Biden's national polling lead, narrowing a 10-point deficit to 5 percentage points, per the RealClearPolitics average. And he has taken a slight lead in Iowa, per FiveThirtyEight.

Yes, but: The interest online hasn't pushed Sanders past Biden in TV coverage. On cable news this month, Biden has been mentioned 9.3k times to Sanders' 7.4k, according to the the Internet Archive Television News Archive.

Sanders does hold an edge on network evening news telecasts, with 195 mentions to Biden's 157.

The big picture: The interactions numbers speak to a level of grassroots enthusiasm that often can't be fully captured by polling.

Between Jan. 1 and Nov. 1 of 2016, Trump generated 62% more interactions than Hillary Clinton, despite consistently trailing in the polls.

Our 2020 attention tracker is based on data from NewsWhip exclusively provided to Axios as part of a project that will regularly update throughout the 2020 campaign.

See all past editions of the tracker here.