Senate elections 101: Colorado could come down to women's issues.

Democratic Sen. Mark Udall has dumped much of his campaign money into attacking Republican Rep. Cory Gardner on reproductive rights. But it might not have worked as well as he hoped.

The Monitor's "Senate elections 101" series looks at the specific issues that will be driving voters in each of the 10 tossup races.

The dominant theme of an unpredictable Colorado Senate race has been reproductive rights – an issue that was the focus of Sen. Mark Udall’s very first campaign ad back in April.

Senator Udall, the Democratic incumbent, has painted his Republican rival, Rep. Cory Gardner, as an extreme conservative who would roll back reproductive rights. Congressman Gardner has fought to moderate his positions, opposing a “personhood” initiative on the ballot in Colorado this year – though he supported similar initiatives twice before – and writing an opinion article that calls for over-the-counter sale of contraceptives.

Udall’s focus on reproductive rights, almost to the exclusion of other issues, may have backfired, and while current polls give him an advantage among women, the gender gap isn't the size he likely needs to win the election.

“This is Udall’s gamble,” says Seth Masket, a political scientist at the University of Denver. “This is this nice wedge issue that is designed to peel off moderate-to-conservative women who nonetheless consider themselves pro-choice. It’s something where Democrats have had some success in Colorado, and he’s going all in on that strategy.”

Udall had a slight edge for a while this summer, but recent polls have given that edge to Gardner. Most are still within the margin of error, and voter turnout and a good ground game – historically a strength for Democrats in the state – could play a big role in determining the outcome.

Perhaps surprisingly, almost no other issue has come into play in Colorado in a significant way. Issues that were expected to figure prominently – immigration, energy, and the Affordable Care Act – have largely been a nonentity. Most voters still list the economy as their top issue, but it’s not clear which candidate that’s benefiting.

“To the extent they think the economy is improving, they’re leaning more Democratic in their votes, but a fair number of voters are just not satisfied with the level of improvement,” says Professor Masket.

As many other tossup states, this election may well come down largely to an issue outside of the candidates’ control: how voters feel about President Obama.

“The Democrats believed that the issue that would get them through this was reproductive rights, and they really poured money into it, probably too much,” says Denver-based pollster Floyd Ciruli. “The Republicans really have just one message: [Udall] votes 99 percent with the president.”

Please read our other entries in this series:

• Louisiana is a referendum on Mary Landrieu
• Colorado could come down to women's issues
• Kentucky conflicted about Mitch McConnell
• Iowa split between two very different candidates
• Georgia could turn on a David Purdue gaffe
• North Carolina wary of Tillis's tea party revolution
• Arkansas considers ending its blue-state legacy
• Alaska's remotest places could be crucial
• New Hampshire shapes up as carpetbagger vs. rubber stamp 
• The big Kansas issue Pat Roberts isn't talking about