A new Des Moines Register poll out on Sunday shows the Senate race between Republican Joni Ernst and Democrat Rep. Bruce Braley to be virtually tied with a little more than 3 weeks before the election.

Iowa's blitzkrieg U.S. Senate race is now a 1-point contest: Republican Joni Ernst is at 47 percent, and Democrat Bruce Braley is right at her heels at 46 percent with likely voters, a new Iowa Poll shows.

As armies of Democratic activists go door to door urging Iowans to fill out absentee ballots, they're piling up votes for Braley, who was 6 points down just two weeks ago.

"Braley's catching up," said J. Ann Selzer, the pollster for The Des Moines Register/Bloomberg Politics Iowa Poll, which was conducted Oct. 3-8.

But Ernst has made gains, too. She's 3 percentage points higher than two weeks ago, when she was at 44 percent.

The new poll reveals three potential reasons why this race has tightened in the final sprint:

• The Democrats' aggressive early voting push is aiding Braley, an eight-year congressman from Waterloo. They're rounding up ballots from Iowans who would not otherwise have voted.

• A majority of Iowa likely voters appreciate having a U.S. senator from each political party. Retiring Democratic U.S. Sen. Tom Harkin, 74, has been an old-school liberal street fighter for Iowa for 30 years. And Republican U.S. Sen. Chuck Grassley, 81, who intends to keep adding to his 33 years in the Senate, is a conservative powerhouse.

• Likely voters find more of Braley's policy positions closer to their own views than Ernst's positions among 10 issues tested. A majority of likely voters favor six of Braley's stances to four of Ernst's.

The number one reason Braley has climbed back into the race is that the natural political equilibrium in Iowa is re-establishing itself. There are more Democrats in the state than Republicans, and early voting is proving that point.

Both candidates are heading for the finish line fairly evenly matched in cash available and organization. I'd hate to think the race will be decided by early voting but it is entirely possible that Braley wins based on that factor.