A new poll in Indiana’s U.S. Senate race shows its too close to call.

The new poll of likely voters from SurveyUSA and the Mike Downs Center for Indiana Politics, released Monday, shows Democratic incumbent Joe Donnelly with 41 percent and Republican Mike Braun with 40 percent. Libertarian Lucy Brenton has 8 percent.

A poll summary noted that the race could be decided based on which candidate Brenton pulls voters from and who undecided voters pick on Election Day. The poll's margin of error is 4.6 percentage points.

Donnelly leads with female voters and voters younger than 50, while Braun leads with white voters. For voters older than 50, Donnelly and Braun are tied with 42 percent each.

Braun leads with voters who have a high school education, and Donnelly leads with those who are college-educated.

In the suburbs—where some political observers say races could be decided this year—Donnelly and Braun are practically tied for support, with Braun at 42 percent and Donnelly at 41 percent.

The online poll was conducted from Oct. 12-16 and reached 816 likely voters.

Indiana's U.S. Senate race is among a handful being watched on a national level, as Democrats see it as a must-win to take control of the U.S. Senate or keep Republicans at a slim majority. Republicans view the seat as one that is likely to flip to their party because President Donald Trump won Indiana by nearly 20 points in 2016.