Washington (CNN) Democrats once again hold a wide advantage in a generic congressional matchup, according to a new CNN poll conducted by SSRS , backed by a base of supporters who are more enthusiastic than Republican partisans and more motivated by core issues.

The poll finds 54% of registered voters say they back a Democrat in their congressional district, 38% say they back a Republican. That's a shift in favor of the Democrats since January, bringing their advantage in a hypothetical generic matchup to about the same level as early 2006, a year in which the party won control of both the House and the Senate.

This also mirrors their advantage on the question last fall, before a January full of good economic news brought a shift toward more positive numbers for both President Donald Trump and his party. The same poll also found Trump's approval rating declining -- a metric that's frequently closely tied to his party's performance in a midterm election year.

Democrats and Democratic-leaning independents remain more enthusiastic about voting this fall than Republicans and Republican-leaners. Overall, 51% of that Democratic base say they are extremely or very enthusiastic about voting in November compared with 41% of the Republican base.

The poll also suggests that the issues on which Republicans have largely pinned their electoral hopes -- the economy, taxes and immigration -- are carrying less weight with voters than are health care and gun policy -- two issues where the Democrats typically have stronger backing from the public overall.

Health care and gun policy are deemed deeply important by about half of voters (53% and 49%, respectively, call them extremely important), while about four in 10 say they are as motivated by the economy (43%) and immigration (38%). Sexual harassment is a sharp motivator for 36% of voters. Taxes, an issue Republicans have said will move voters as they realize the benefits of the tax changes passed last year, is extremely important for 35%. The investigation into Russian meddling in the 2016 election rounds out the list, with just about a quarter (26%) calling that extremely important to their vote.

There are wide partisan gaps on how important several issues are to voters, with Democratic voters more likely to say they are particularly moved by health care (65%, vs 40% among Republicans), gun policy (62%, vs. 40% among Republicans), sexual harassment (50%, vs. 21% of Republicans) and immigration (48%, vs. 32% among Republicans).

Republican voters, however, are not significantly more motivated than Democrats on any issue tested, suggesting that more positive views of the economy and the GOP's success in enacting tax reform, which may have been boosting their numbers in January, may be less strong a motivator for the party's voters this fall than are the issues where Democrats have focused their opposition to the Republican-led government for that party's base.

Gun policy in particular has increased dramatically in salience compared with the previous midterm election cycle. In October 2014, ahead of the first election after the mass shooting at an elementary school in Newtown, Connecticut, just 28% of voters described that issue as extremely important to their congressional vote. Now, 49% say the same. The numbers have risen across party lines, but most dramatically among Democrats. In 2014, 31% of Republican voters called gun policy extremely important to their vote. Now, 40% do. Among independents, it's risen from 27% to 42%. And among Democrats, that share has climbed a whopping 34 points from 28% to 62%. Overall, those who call the issue a critical one for their vote are supporters of stricter gun laws by an 80% to 19% margin.

Many voters also say their votes may be swayed by the types of donations a candidate accepts on gun policy. Asked whether a donation from the National Rifle Association would dissuade them or encourage them to support a candidate for Congress from their own district, 45% say they'd be less apt to support a candidate who accepted an NRA donation, 14% more likely, and 39% say it wouldn't make a difference. The effect is sharpest among Democrats, 80% of whom say they'd be less inclined to back such a candidate.

On the other side of the coin, 37% say a donation from a group advocating for stricter gun laws, such as Everytown for Gun Safety, would make them more apt to back that candidate, 26% would be less likely to support a candidate who accepted such a donation and 34% say it wouldn't move their vote.

It is early in the cycle, however, and much can change between now and November. Past polling suggests increases in concern about gun policy seen in surveys conducted shortly after mass shootings often fades over time.

The CNN poll was conducted by SSRS February 20-23 among a random national sample of 1,016 adults, including 909 registered voters, reached on landlines or cellphones by a live interviewer. Results for the full sample have a margin of sampling error of plus or minus 3.7 percentage points, it is 3.9 points for registered voters and larger for subgroups.