A new Rasmussen Reports telephone survey of likely Colorado voters finds Norton still the strongest of three Republican hopefuls against either of the candidates who hopes to be the Democratic nominee.

Norton leads Bennet 51% to 37%, a two-point gain for her from last month.

She runs just seven points ahead of Romanoff, a former state House Speaker who is challenging Bennet for the Democratic Senate nomination – 45% to 38%. In January, Norton had a 12-point lead, 47% to 35%.

For the two most prominent Republicans challenging Norton for their party’s nomination, ex-state Senator Tom Wiens and Ken Buck, a country district attorney, the contest with either Democrat is much closer.

Wiens leads Bennet 45% to 40% and is in a virtual tie with Romanoff, 42% to 40%.

Buck for now beats Bennet 45% to 41% and Romanoff 45% to 39%.

The numbers are roughly comparable to those from last month and both Democratic hopefuls seem locked into the 35% to 40% range for now, regardless of their GOP opponent.

But while Norton’s lead on Bennet has steadily grown in polling since last September, she continues to hover in the mid-40s against Romanoff, suggesting that incumbency may be one of Bennet’s biggest problems. Given voter unhappiness with the national health care plan and the state of the economy, a number of Democratic senators are experiencing a similar challenge.