Mr. Hickenlooper, who is mired at the bottom of public polling of the presidential race, hopped into Senator Michael Bennet’s car on Friday night in this Northern Iowa town to discuss his impending decision, said Democrats familiar with the discussion, who, like others, spoke on the condition of anonymity to describe confidential talks.

The two drove around Clear Lake for about 20 minutes ahead of the Wing Ding dinner, a Democratic fund-raiser that drew 21 presidential candidates. Aides and advisers to the two men, who have been both allies and rivals over their careers in Colorado politics, declined to reveal what was discussed.

Officials who have been in discussions with the Hickenlooper campaign said Tuesday that the former two-term governor is giving serious consideration to switching to the Senate race but stressed that a final decision has not yet been made. Short of a massive change in political momentum, Mr. Hickenlooper is certain to fail to qualify for the next round of presidential debates in September, an additional blow to a campaign struggling to attract attention and financial contributions.