President Barack Obama holds clear leads over Republican challenger Mitt Romney in three more swing states, according to new NBC News/Wall Street Journal/Marist College polls.
In Wisconsin, home base of Romney's running mate Paul Ryan, the Democratic incumbent leads among likely voters by 50 percent to 45 percent.
And in Iowa, whose heartland caucuses launched both men's presidential bids, Obama holds a wider 50 percent to 42 percent edge.
The polls, conducted this week amid controversy over Romney's secretly recorded remarks at a fundraiser earlier this year, represent a blow to the Republican ticket. (Read More: Romney Derides Obama Supporters in Damaging Video.)
Wisconsin (10), Colorado (9) and Iowa (6) hold 25 electoral votes that Romney badly needs to take away from Obama, who won all three states four years ago.
Together with Ohio, Florida and Virginia — where NBC/WSJ/Marist polls last week also showed Obama leading — these states represent two-thirds of the nine battlegrounds that the two presidential campaigns are most seriously contesting.
In two others, Nevada and New Hampshire, the average of recent public polls also shows Obama in the lead. North Carolina is the only one of the nine where Romney holds an edge. (Read More: Why Obama's Up in Swing States Despite Bad Economy.)
The new surveys show that, with Wisconsin, Colorado and Iowa voters, Obama has neutralized Romney's claim to superior ability to improve the American economy. In all three, voters rate Obama even or ahead of the former Bain Capital executive on the issue.
On balance, Wisconsin voters look favorably upon Ryan, with 49 percent expressing positive views, 40 percent negative. But the poll contains little evidence that the House Budget Committee chairman's signature approach to overhauling Medicare is benefiting Romney with the critical senior citizens' constituency. (Read More: Ryan's Way: How He Would Change Medicare.)
While national surveys show Romney leading with elderly voters, in Wisconsin Obama leads by 48 percent to 46 percent among likely voters age 60 or older. In Colorado, Romney leads by 50 percent to 45 percent with that group; in Iowa, Obama leads 48 percent to 44 percent.
The building blocks of Obama's lead match his core constituencies nationally. Among women, Obama leads in all three swing states by margins ranging from 12 percent to 18 percent; Romney's lead among men, which ranges from 2 percent to 5 percent, isn't enough to pull the Republican ticket even.
Among likely voters under age 30, Obama draws an overwhelming 70 percent support in Colorado to Romney's 25 percent. In Wisconsin, the president's lead among young voters is 56 percent to 38 percent. Only in Iowa, where Obama leads with young voters by 50 percent to 44 percent, does Romney draw within single digits among that group. (Read More: Romney-Ryan Ticket Opens the GOP’s Door to Younger Voters.)
All three NBC/WSJ/Marist surveys were conducted Sept. 16-18. The margins for error for likely voter results were 3.2 percentage points in Wisconsin, 3.1 percentage points in Colorado and 3.3 percentage points in Iowa.
—By CNBC's John Harwood
"Key companies located/doing business in Wis.: Oshkosh (Corp.) and Harley-Davidson . Key companies located/doing business in Colorado.: Molson Coors Brewing . Key companies located/doing business in Iowa: ConAgra and Archer Daniels Midland .
Key companies located/doing business in Colorado.: Molson Coors Brewing .
Key companies located/doing business in Iowa: ConAgra and Archer Daniels Midland .