It is said there's someone for everyone. Who would have predicted, when Todd Akin, the Republican representative, was abandoned by his party for his "legitimate rape" comments a month ago, Newt Gingrich would be his knight in shining armour.

But at the first major fundraising event held by the Akin campaign since the Missouri senate candidate was blackballed by the party funders and leaders, Gingrich pledged his support and said he was just the first in a wave of well-known Republicans to stand by Akin.

Republican party leaders have said the controversial remarks have made it impossible for Akin to unseat incumbent US senator Claire McCaskill. They have pleaded with him to step down in time to name a replacement for the election.

Gingrich came to Missouri on Monday to back Akin at a $500-a-ticket fundraising lunch, at which he addressed about 50 of the congressman's supporters – and earlier, the media.

At at a press conference at a train station in Kirkwood, a suburb of St Louis, Missouri, Gingrich said Akin was running a winnable race and made his own prediction – that the national Republican leaders, including Mitt Romney, would reverse track and back the candidate once they "adjust to the reality" that he is staying in the race.

"If Todd and the people of Missouri prove it's a close race, what's the moral case for not backing the Republican nominee?" Gingrich said.

Gingrich told the crowd, made up of reporters and a handful of supporters that it all came down to a simple question. "Do you want to keep Harry Reid as the majority leader?" Gingrich said to shouts of "No" from Akin supporters.

Gaining McCaskill's seat is seen as vital if the GOP is to take over the Senate in November. "How do you go back to your donors and say: 'Let's throw the Senate away?'," Gingrich said.

The former presidential candidate dismissed comments on Sunday by Republican national committee chairman Reince Preibus who declared on TV that there was no way any RNC money would be used to help Akin. "My expectation would be that in the crunch, in October, governor Romney is going to be for the entire ticket, and he's going to be for Todd Akin," Gingrich said.

He compared Akin to Harry Truman, senator and later president who was dumped by the party machine in the 1940s.

The fundraiser would have netted Akin up to $42,000 from the cost of the tickets alone, in addition to the $600,000 Akin has already raised online.

Rick Tyler, a former longterm aide to Gingrich, who is now advising Akin, said he had "adequate funding" to fight the election.

The polls are showing a close contest, and Tuesday is the last day that Akin could seek a court order to drop out. On Monday, he reaffirmed that he had no plans to withdraw, telling supporters that a number of prominent Republicans have already agreed to campaign on his behalf but declining to name names. He begins a four-day "Common Sense" bus tour.

Akin has aplogised for the remarks on "legitimate rape" he made in a televised interview and has even drummed up a "Women for Akin" group. A video on his website has one woman weeping as she recounted having an abortion as she endorses the pro-life candidate she said speaks up for women.

His supporters say he a mistake and should be forgiven for it. Paula Ritter, 78, who was at Kirkwood station with her husband to support Akin said he and other politicians needed to learn "who they are talking to". "I think he's sorry. But I don't think he's sorry for thinking that" she said. Ritter said she didn't agree with him "but I wouldn't change my vote because of it. I'm not for single-issue politics".

Gingrich joked: "if saying something dumb disqualifies you, Joe Biden couldn't be vice-president."

About 50 people gathered outside the fundraiser to protest Akin's candidacy. Photograph: Karen McVeigh/The Guardian

Akin's comments stirred up a wave of outrage and added to the perception of the so-called "war on women" among conservative Republicans.

Outside the Branica restaurant where the former House speaker addressed some 50 Akin supporters, a similar-sized crowd had gathered to protest. One held up a banner which said: "Lets shut Todd Akin down" in reference to his comments that rape victims had a way of "shutting down" pregnancies.

Jane Von Kaenel said his remarks had re-invigorated the feminist base in Missouri. "He's an embarrassment, he's out of touch," she said of Akin. "You just can't hold your nose and get away from the smell." She said she thought that "many, many" Republicans would vote for McCaskill.

Susan Cunningham, 73, a retired teacher from Pacific, in Franklin, Missouri, who was holding the banner declaring "Let's shut down Todd Akin" said she was worried about Republican party becoming more and more conservative on social issues. She said: "I'm very worried about what is happening in this country. I'm against Todd Akin's voting record on everything, from women's issues, to the environment and education."

"I don't understand why Newt Gingrich is supporting him, but to be honest I don't understand why Newt Gingrich does anything. Newt must have an ulterior motive. They are blowing smoke and they are very good at it. But Todd Akin is scary. When I think of my daughter and my grandchildren, are they going to have access to birth control of are they going to have to put a veil on? It's crazy here, we are going backwards."

Gingrich refused to say what conversations he had with the party leadership that led him to predict a u-turn on Akin.

Asked if anyone from the party had tried to stop him from coming out in support of Akin, he said: "I'm not going to talk about my conversations with party leadership."

Tyler, a former long-term aide to Gingrich who now works for Akin, said he thought the candidate would raise an "adequate amount" of money to stay in the race, but added that he believed if would be "political malpractice" if the Republican party did not get back behind him.

Marsha Walker, a social worker from Chesterfield, who attended the fundraiser, said she hoped the voters would forgive Akin his remarks. She said she was voting for him because of his strong pro-life views.

"Everyone who has spoken has erred in some way, and not to forgive is unforgivable. We need someone like Todd to fight for morality in Washington, and Todd is s a fighter."