With Primary Day being held tomorrow, PolitickerCO.com takes a look at the four competitive state Senate primary races in Colorado. 

4th SENATE DISTRICT (Republicans)

OPEN SEAT: State Sen. Tom Wiens (R-Castle Rock) is not running for re-election

Candidates:

• Bob Denny: Retired Air Force Colonel from Glen Eagle
• Mark Scheffel: Attorney and a former Douglas County Republican Party Chair from Parker

Overview: The seat opened up unexpectedly in April when Wiens, a potential '10 gubernatorial candidate, announced he wouldn't seek re-election. SD-4 was designed for Scheffel to run in 2004, though he dropped out then when Wiens entered the race. This time, Scheffel has name recognition and endorsements from A-listers such as Tom Tancredo, and picked up 65 percent of delegates' votes at the SD-4 assembly. Denny has the financial edge, raising $25,000 to Scheffel's $18,300.

What to look for: A Scheffel win, but perhaps by not as much as in the assembly. As a former DougCo GOP chair, he has the establishment support and the name recognition that Denny, a political newcomer, lacks. But Denny has run a smart and energetic  -- albeit limited -- campaign and is making a late run at making the race competitive.

18th STATE SENATE DISTRICT (Democrats)

OPEN SEAT: State Sen. Ron Tupa (D-Boulder) is term-limited

Candidates:

• Cindy Carlisle: University of Colorado regent from Boulder
• Rollie Heath: 2002 gubernatorial candidate from Boulder

Overview:  With Heath's name recognition, on paper it looks like it's his race to lose. But Carlisle has significant support in the CU community - despite supporting Bruce Benson as a finalist for CU president, among other things -- and the political winds of "change" would seem to favor her.

What to look for: Many insiders say the race is too close to call. High voter turnout favors Carlisle.

24th STATE SENATE DISTRICT (Republicans)

OPEN SEAT: State Sen. Steve Ward (R-Littleton) is running for Congress

Candidates:

• Jerry Call: University of Denver professor and South Suburban Parks and Recreation District Board chair from Littleton
• Lauri Clapp: Former state representative from Centennial

Overview: Clapp has a big endorsement list, a financial edge, and name recognition from her four state House terms. Call has tried to turn her legislative experience into a negative, pointing out Republicans lost the state legislature and governor's seat during her term of office.

What to look for: A Clapp victory. Her eight years in the state House give her campaign experience and great name ID.  

35th STATE SENATE DISTRICT (Democrats)

OPEN SEAT: Senate Majority Leader Ken Gordon (D-Denver) is term-limited

Candidates:

• Joyce Foster: Former Denver City Council president from Denver
• Alice Borodkin: State representative from Denver

Overview: Foster has raised double the money Borodkin has and won the SD-35 assembly with nearly 70 percent of the vote. Borodkin has significant labor support and has been endorsed by Marshall, the outgoing incumbent. The race has gotten heated as both candidates have taken to the offensive over ethics.

What to look for: A Foster win. Insiders say she's run a well-organized campaign, though her margin of victory will likely be smaller than the assembly results.

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