VIDEO-CNN Poll: Biden and Trump matchup tightens as enthusiasm hits new high - CNNPolitics

(CNN)Joe Biden's lead over Donald Trump among registered voters has significantly narrowed since June, according to a new CNN poll conducted by SSRS, even as the former vice president maintains an advantage over the President on several top issues and his choice of California Sen. Kamala Harris as a running mate earns largely positive reviews.

And on the eve of

, a majority of voters (53%) are "extremely enthusiastic" about voting in this year's election, a new high in CNN polling in presidential election cycles back to 2003.

Overall, 50% of registered voters back the Biden-Harris ticket, while 46% say they support Trump and Pence, right at the poll's margin of error of plus or minus 4 percentage points. Among the 72% of voters who say they are either extremely or very enthusiastic about voting this fall, Biden's advantage over Trump widens to 53% to 46%. It is narrower, however, among those voters who live in the states that will have the most impact on the electoral college this fall.

Across 15 battleground states, the survey finds Biden has the backing of 49% of registered voters, while Trump lands at 48%.

The pool of battleground states in this poll includes more that Trump carried in 2016 (10) than were won by Hillary Clinton (5), reflecting the reality that the President's campaign is more on defense than offense across the states. Taken together, though, they represent a more Republican-leaning playing field than the nation as a whole.

The movement in the poll among voters nationwide since June is concentrated among men (they split about evenly in June, but now 56% back Trump, 40% Biden), those between the ages of 35 and 64 (they tilt toward Trump now, but were Biden-leaning in June) and independents (in June, Biden held a 52% to 41% lead, but now it's a near even 46% Biden to 45% Trump divide).

Trump has also solidified his partisans since June. While 8% of Republicans or Republican-leaning independents in June said they would back Biden, that figure now stands at just 4%. And the President has boosted his backing among conservatives from 76% to 85%.

But the survey suggests that Trump's voters are a bit more likely to say that they could change their minds by November (12% say so) than are Biden's backers (7%).

More voters say their choice of candidate is about Trump than say it is about Biden. Nearly 6 in 10 say they support the candidate they do because of their view of Trump (29% say their Biden vote is more to oppose Trump, 30% say they are casting a Trump vote in support of him), while only 32% say Biden is the deciding factor (19% are voting in favor of Biden, 13% casting a ballot to oppose him).

Overall, 54% disapprove of the way Trump is handling his job as president and 42% approve. That's an uptick since June, and about on par with Trump's ratings from earlier this year. It still lands the President near the bottom of a list of historical approval ratings for presidents seeking reelection just ahead of their nominating conventions. Trump lands ahead of Jimmy Carter (33% approval) and George H.W. Bush (35%), but below Barack Obama (48%), George W. Bush (49%), Bill Clinton (53%) and Ronald Reagan (54%).

Trump's favorability rating remains underwater nationally (43% see him favorably, 55% unfavorably), a bit worse than Biden's 46% favorable to 47% unfavorable even split. In the battleground states, though, voters' views on the two candidates are almost even: 52% have an unfavorable opinion of Biden, 54% of Trump. Both candidates are viewed favorably by 45% in those states.

Kamala Harris seen as a good pick

Harris joins the ticket with a narrowly positive favorability rating (41% have a favorable view, 38% unfavorable), which is an improvement since May when 32% of Americans said they had a positive view of her and 33% a negative one.

Biden's selection of Harris is rated as excellent or pretty good by most (52%), and 57% say it reflects favorably on Biden's ability to make important presidential decisions. Most say she is qualified to be president should that be necessary (57%). And a majority, 62%, say her selection does not have much effect on their vote. People of color, though, are more likely than White people to say her selection makes them more likely to back Biden (28% among people of color, 18% among whites).

Compared with other recent Democratic running mates, Harris fares well. The 30% who call her selection excellent outpaces the share who said so in CNN polling on John Edwards in 2004, Biden in 2008, Joe Lieberman in 2000 or Tim Kaine in 2016. And the 57% who say she is qualified to serve as president if that becomes necessary is only topped by Biden (63%) and Al Gore in 1992 (64%).

On the issues

The poll suggests that supporters of the two candidates are living in alternate universes when it comes to the issues that matter to their vote. Overall, the economy, coronavirus, health care, gun policy and race relations are rated as extremely important by at least 40% of voters. But there are large gaps between Biden and Trump voters on the importance of these issues. Seventy percent of Biden voters say the coronavirus is critically important vs. 24% of Trump voters. Among Trump backers, 57% rate the economy as extremely important, while 37% of Biden voters agree. Majorities of Biden supporters (57% in each case) call health care and race relations extremely important, while only about 1 in 5 Trump backers agree (20% on health care, 22% on race relations).

Biden tops Trump as better able to handle most of the issues tested in the poll: Racial inequality in the US, the coronavirus outbreak, health care and foreign policy. Trump wins out on handling the economy. Voters are closely divided over which candidate would keep Americans safe from harm (50% say Biden would, 47% Trump). And more generally, Biden is more often seen as having "a clear plan for solving the country's problems" (49% choose Biden to 43% Trump) and as better able to "manage the government effectively" (52% Biden to 44% Trump).

And when it comes to these top issues, nearly all Trump and Biden supporters think their man is the right one for the job. Just 1% of Biden backers say they would trust Trump over Biden to handle racial inequality in the US, and only 2% would trust Trump to handle the coronavirus outbreak. On the flip side, 2% of Trump voters say they would prefer Biden on the economy, and only 4% choose him on the coronavirus outbreak.

Overall, Biden holds the edge on a range of positive traits often seen as valuable in a run for the White House. Most say he cares about people like them (53% Biden, 42% Trump), shares their values (52% Biden to 43% Trump), and is honest and trustworthy (51% Biden to 40% Trump). More also say Biden will unite the country and not divide it (55% Biden to 35% Trump). But in this matchup between two septuagenarians, voters are split over which one has the stamina and sharpness to be president (48% say Trump, 46% Biden).

The CNN Poll was conducted by SSRS August 12 through 15 among a random national sample of 1,108 adults reached on landlines or cellphones by a live interviewer, including 987 registered voters. The survey also includes an oversample of residents of 15 battleground states for a total subsample of 636 adults and 569 registered voters from those states. That subset was weighted to its proper share of the overall adult population of the United States. Results for the full sample have a margin of sampling error of plus or minus 3.7 percentage points. It is 4.0 points among registered voters and 5.4 points for results for registered voters in the battleground states.