Michael Bennet’s pursuit of his own U.S. Senate seat isn’t going to be easy. Republican Ken Buck is leading Democrat Bennet 49-44 among likely voters in the latest poll by CNN/Time magazine (via Talking Points Memo). The worst news of the poll for Bennet and his supporters is that Buck leads by a hefty 14 points among independent voters and holds a nearly five-point lead in a TPM average of several polls. One shred of good news for Bennet: In the CNN/Time poll, Bennet, whose campaign may be helped in October when First Lady Michelle Obama is expected to rally for him, has a 47-44 lead among registered voters.

Forces backing both Buck and Bennet have rolled out aggressive attack ads on television, and it’s unclear from reports what effect those ads are having on voters’ minds. One particularly ominous ad by the Democratic Senatorial Campaign Committee claims Buck wants to rewrite the U.S. Constitution and end Americans’ rights to vote on senators. “Ken Buck’s just too extreme for Colorado,” the ad states.

CNN picks apart the ad, labeling it a “very tall tale,” noting that the allegation stems from a remark Buck made last year at the Pikes Peak Economic Club after being asked about repealing the 17th Amendment, which abolished the selection of U.S. senators by state legislatures after the process became corrupted and instead instituted a popular vote for senators.

Some critics suggest that senators are now so beholden to power brokers and fundraisers in Washington that scrapping the 17th Amendment would lead to a more ethical system. Buck considered the idea publicly, CNN writes, but then a day later called the questioner back and said he wouldn’t repeal the amendment. The commercial does not make that fact clear.