Ever the party loyalist, "I don't regret that," Mukherjee said, when asked if he felt bad that he could not become the prime minister despite his vast experience in politics.
"I'm repeating that Manmohan Singh is one of the finest persons and worthy person to be the prime minister.
"After Neheruji and Indiraji, he will be the next man to complete a second term. So no regret at all."
Mukherjee turned down former Lok Sabha speaker Sangma's call for a debate between the two candidates ahead of the July 19 presidential election.
"(The) issue is not about debate. Debate on what?" asked Mukherjee, who is the candidate of the United Progressive Alliance.
"(The Indian) president is a figurehead. Debate takes place on issues... on the issues determined by the political parties.
"(The) Indian president does not determine policy. Here President is not the policy maker. In the name of the president, the cabinet takes the policy decision."
Mukherjee described Sangma as "a bright man" and said: "Yes, I love him."
The Congress leader came out against conscience vote -- which Sangma has advocated in a bid to overcome his numerical disadvantage in the electoral college.
"What is conscience vote? When the party decides, is the member going to say it's against his conscience!"
Mukherjee, whose candidature also has the support of the Left, Shiv Sena and Janata Dal-United, filed his nomination for the presidential post Thursday.
Although an election will be held, Mukherjee is tipped to win.
He said coalition politics arose out of necessity. "(The) compulsion is ... because you can't go for a general election every day."
Mukherjee said he would continue to appeal to West Bengal Chief Minister and Trinamool Congress leader Mamata Banerjee to back his candidature.
"I hope she will take that decision at the appropriate time. I appeal to her to extend support to me."
He said when the debate over a presidential candidate was raging, he told Congress president Sonia Gandhi "that what(ever) role will be assigned to me I will discharge that faithfully.
"Thereafter (after) having discussions she decided... Then things followed."
What is the secret behind the wide support for him?
"As a political activist we talk to each other and we interact with each other," he said. "Therefore there are many people who have many friends in all political parties. I'm not the exception."
