Donald Trump has reduced Hillary Clinton's national lead to just three points—down from five last week—underscoring the grim prospects of the presidential election, a new poll released on Tuesday reveals.

The NBC News/SurveyMonkey poll finds that Clinton now leads Trump nationally 48 to 45 percent, an unsettling development as the candidates enter their final stretch of primaries, two of which are taking place Tuesday in Kentucky and Oregon. Last week, Clinton and Trump were found to be in a dead heat in three swing states.

Politico reports:

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Clinton dominates among minority voters. The Democratic front-runner leads Trump by a 75-point margin among black voters, 84 percent to 9 percent, and holds a 37-point advantage among Hispanic voters, 65 percent to 28 percent. Women also favor Clinton, while Trump leads among men and white voters.

The survey also notes that Clinton's rival, Bernie Sanders, beats Trump by 53 to 41 points in a hypothetical match-up—a much wider margin than the former secretary of state.

Sanders' campaign manager Jeff Weaver said Tuesday that the Vermont senator will work "seven days a week, night and day," to ensure Trump does not win the presidency.

The poll was conducted online May 9 - May 15, surveying 14,100 adults, including 12,507 registered voters. It has a margin of error of +/- 2 percentage points.