After an ugly and personal campaign, the Republican primary for Senate between former Lt. Gov. Jane Norton and prosecutor Ken Buck is too close to call heading into Election Day.

Final numbers from Public Policy Polling out Monday have Norton leading Buck 45 percent to 43 percent, with 12 percent undecided.

Sen. John McCain (R-Ariz.) made two campaign stops for Norton in Colorado Sunday as the candidate made her closing pitch to voters. She used McCain as a proxy to suggest Buck isn't as committed to the wars in Iraq and Afghanistan. 

Buck has worked to paint Norton as the pick of the GOP establishment and is backed by many Tea Party groups in the state. 

Among the 35 percent of likely Republican primary voters who called themselves members of the Tea Party movement, Buck leads that group by seven points. Among the 47 percent of likely voters who don't consider themselves members of the Tea Party, Norton holds a seven point lead. 

The poll surveyed 767 likely voters and has a margin of error of plus-or-minus 3.5 percentage points. 

On the Democratic side, Sen. Michael Bennet leads former state House Speaker Andrew Romanoff 49 percent to 43 percent, with 9 percent undecided. 

Bennet has had the support of the White House, while Romanoff won the backing of former President Clinton.

The Democratic primary poll surveyed 448 likely voters and has a margin of error of plus-or-minus 4.6 percentage points. 

The wildcard in both of these races is the role early voting will play in the process. In most of the state's 64 counties the election is mail-in only, with the secretary of state's office estimating that well over half of voters have already cast a ballot ahead of Election Day.