A new poll indicates that Republican Jeff Flake remains the front-runner in the race to replace Jon Kyl in the U.S. Senate.

But, the six-term U.S. Congressman’s lead appears to be shrinking over Republic challenger, Wil Cardon, shows a poll from Public Policy Polling.

Flake leads Cardon by a 42-20 margin in a survey of 500 Arizona voters done last week. That’s a huge lead, but smaller than the 49-point margin he had on Cardon in a February poll done by Public Policy Polling.

While still a monumental gap to close, the president of Public Policy Polling said Cardon’s improvement since the last poll is noteworthy.

“This race is starting to show some of the upset potential that has characterized many Republican Senate primaries over the last two cycles,” said Dean Debnam, president of Public Policy Polling in a press release.

The poll shows both Flake and Cardon lead Richard Carmona, the presumptive Democratic nominee. Flake’s lead, 48-25, is much larger than Cardon’s lead on Carmona, which is 40-37, the poll shows.

Carmona, the former U.S. Surgeon General, made tiny gains since Public Policy Polling’s last survey about this race in February. In that poll, Flake led Carmona by 11 points and Cardon led Carmona by four points.

Carmona remains largely unknown, with only 34 percent of the people surveyed having an opinion about him. Flake, by comparison, is recognized by 60 percent of the people surveyed.

A positive for Carmona, however, is that voters who know both Carmona and Flake strongly favor Carmona, the polls shows.

“As Carmona continues to campaign and become a known commodity to the rest of the electorate, he can close the gap,” says a press release from Public Policy Polling.

Stay tuned to the Pueblo Politics blog throughout 2012 for news, updates and information about Arizona politics. You can follow Arizona Daily Star reporter Brady McCombs on Twitter by clicking on his name.