Rep. Dennis Kucinich (Ohio) is vowing to remain the sole challenger to Sen. John Kerry (Mass.) in the Democratic presidential race, even though Tuesday’s Illinois primary formally shut down the former Cleveland mayor’s chances of winning the nomination.

Kucinich, the liberal maverick who entered the race on an anti-war platform, said in a telephone interview this week that he will keep stumping through the July Democratic National Convention in Boston.

He acknowledged that he cannot beat Kerry for the nomination, but he wants to keep his issues alive and talk to voters about his positions on fair trade policies, universal health care and the war in Iraq.

“I am in all the way to the convention, absolutely,” said Kucinich, who has collected 23 delegates but failed to win any state’s primary or caucus.

The Ohio lawmaker’s pledge comes just after the Rev. Al Sharpton, who with Kucinich had the lowest delegate count in the race, abandoned his bid for the White House and endorsed Kerry. It also comes on the heels of the Illinois primary that officially gave the Massachusetts Senator enough delegates to win the party’s nod.

“I understand that Senator Kerry has amassed the number of delegates that are sufficient to gain the nomination and that question appears to be on its way to being decided in Boston,” Kucinich said. “But what remains to be decided is the direction of the Democratic Party and the direction of this country.”

Kucinich said he doesn’t believe his continued candidacy hurts Kerry, saying one could argue the primary process is too “frontloaded” and that continuing the issues debate “can only help the party.”

He then said firmly he would not endorse Kerry or any other candidate before the convention, saying: “That’s premature. I’m an active candidate. I’m not going to discuss that. I’m still a candidate.” He added that he hadn’t been contacted by anyone with the Kerry campaign seeking his endorsement.

As for Ralph Nader, the longtime consumer advocate running as an Independent presidential candidate, Kucinich also brushed off talk of throwing his support in that direction. At the same time, however, Kucinich said he and Nader — a 2000 Green Party presidential hopeful who many argue sunk Democrat Al Gore’s chances for the White House — share a similar constituency base.

“I may well be one of the few people in the party who has the ability to attract the very voters Nader would attract,” he said. “It is very important for Democrats to have people in this party who have the ability to reach out to those people.”

Kucinich vowed early on in his campaign to stay in the race until the bitter end, but later acknowledged that at some point he may re-evaluate his status if it became mathematically impossible to win. His plan now, he said, is to continue 12 more weeks of active campaigning. He is scheduled to be in Alaska today.

“I’m taking it one step at a time right now,” he said. “I am in the race and I am apparently the only active candidate [besides Kerry].”