DENVER -- The presidential campaigns bombarded voters with visits, phone calls and last-minute advertising Monday, an indication of how critical they believe Colorado's nine electoral votes could be on Election Day.

Since 1976, a Democratic presidential candidate has won Colorado just once -- Bill Clinton in 1992. Al Gore in 2000 and John Kerry in 2004 each lost to George W. Bush.

Both parties targeted Colorado in 2004 but Democrats pulled support for John Kerry before the election and he lost the state by 100,000 votes, political consultant Eric Sondermann said.

"Ask Al Gore or John Kerry if they would have wanted nine electoral votes. Those nine electoral votes would have made Al Gore president," the bipartisan Sondermann said Monday. "I'm unaware of any historical precedent for Colorado being this much in play."

Colorado offers Republicans a better chance of success than other target states like Pennsylvania, Ohio and Virginia, where Democrat Barack Obama has bigger leads in polls, political consultant Floyd Ciruli has said.

Today, the electorate is just about evenly divided among Republicans, Democrats and unaffiliated voters. Voter turnout already has been intense with 1.6 million mail-in ballots and 365,000 absentee ballots turned in from the state's 2.6 million active registered voters. The statewide turnout is expected to set a record, exceeding 90 percent.

In the presidential race, Obama has led Republican John McCain by single digits in recent polls.

And, the campaigning continues at a fever pitch.

On Monday, GOP vice presidential candidate Sarah Palin was headed to Colorado Springs for an afternoon rally while Michelle Obama planned to visit a high school in a southwest Denver suburb. McCain is to visit Grand Junction on Election Day, just four days after Obama held a rally in Pueblo.

Other closely watched races drawing voters to the polls include the U.S. Senate race between Democrat Mark Udall and Republican Bob Schaffer to replace retiring Republican Wayne Allard.

Supporters of Schaffer and Udall targeted voters with last-minute phone calls and door-to-door visits.

In northeastern Colorado, GOP incumbent Marilyn Musgrave and Democratic challenger Betsy Markey are in a hard-fought race in the 4th Congressional District. There also are a number of contested ballot issues: a proposed constitutional amendment would define a person "to include any human being from the moment of fertilization;" an amendment to eliminate a credit that allows oil and gas companies to deduct property taxes from their severance taxes and a number of labor-related measures.