John Merline of Investor’s Business Daily reports an interesting development in the Democratic presidential nomination contest.

With just 21 days until the presidential primaries officially begin in Iowa, Hillary Clinton’s support among Democrats nationally has taken a serious tumble, falling eight points to 43%, according to the latest IBD/TIPP Poll. Support for her chief rival, Bernie Sanders, climbed six points to 39%.

As a result, Clinton’s lead over Sanders, which had been 18 points, is now just 4 points.

Other polls have shown the race tightening in Iowa, which holds its caucuses on Feb. 1, and New Hampshire, which has its primary eight days later. Two recent New Hampshire surveys have Sanders in the lead, and the latest NBC poll in Iowa has Sanders just three points behind Clinton.

But the IBD/TIPP Poll is the first to show the race significantly tightening nationwide.

Clinton, in response to her sagging poll numbers, has started to turn up the heat on Sanders, after all but ignoring the self-described socialist whose maverick campaign has been surprisingly resilient. CNN reported over the weekend that “a sense of anxiety is cascading through Hillary Clinton’s campaign” over Sanders’ gains.

Clinton recently attacked Sanders on his position on gun control, and released a campaign ad in Iowa and New Hampshire asserting that she is “the only one” who can beat whoever the Republican Party nominates.