With the Iowa caucus less than a week away, Hillary Clinton and Donald Trump remain the strong front-runners of their respective parties nationally.

Trump maintains his lead with 39% support among Republican and Republican-leaning voters — a full 20 points higher than any other Republican candidate.

On the Democratic side, Clinton is holding steady among Democratic and Democratic-leaning voters at 51% — she maintains a 14-point lead over Sanders, who has 37% support nationally.

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These results are according to the NBC News|SurveyMonkey Weekly Election Tracking poll conducted online from January 18, 2016 through January 24, 2016 among a national sample of 9,690 adults aged 18 and over, including 8,215 who say they are registered to vote.

Support for Clinton and Sanders has remained nearly unchanged over the month of January in our tracking poll. But after the first caucus, national numbers may shift to reflect changes in momentum between candidates.

There has been a lot of discussion about how national polling numbers will translate into the early states like Iowa and New Hampshire. This is where an analysis of demographics is useful. In the Weekly Election Tracking poll, Clinton has maintained a double-digit lead over Sanders among women in the last four weeks. This week, 57% of women voters support Clinton, and only 31% of women voters support Sanders.

Young voters, however, still support Sanders over Clinton, regardless of gender. Overall, 68% of 18-24 year-old voters support Sanders, compared to only 21% of 18-24 year-old voters who support Clinton.

White voters support Clinton and Sanders equally, each with 45% support. African-American voters are more likely to support Clinton over Sanders, 65% to only 20%, but non-white turnout in the 2008 Democratic Iowa caucus was only 7%.

Trump is still far ahead in the Republican field, with 39% support among Republican and Republican-leaning voters. Cruz has 17% support, dropping 4 points from last week. The senator may have lost ground this week amid questions about his eligibility to run for president. Rubio has 10% support, while Carson and Bush hold unchanged from last week with 8% and 4%, respectively.

Trump continues to dominate the field across all age groups and among male and female voters. The biggest shift in our results this week is among white evangelical voters — a key group in the 2012 and 2008 Iowa Republican caucuses. Trump gets 37% of support, while Cruz is second with 20% support. He drops 9 points from last week among this demographic. Carson and Rubio are nearly tied in this group — 11% and 10%, respectively.

The NBC News|SurveyMonkey Weekly Election Tracking poll was conducted online from January 18, 2016 through January 24, 2016 among a national sample of 9,690 adults aged 18 and over, including 8,215 who say they are registered to vote. Respondents for this non-probability survey were selected from the nearly three million people who take surveys on the SurveyMonkey platform each day. Results have an error estimate of plus or minus 1.3 percentage points. A full description of our methodology and the poll can be found here.