(Christian Gooden | AP)

Rep. Todd Akin has vowed to continue his run for Missouri's Senate seat, despite Republican party demands that he step aside. He also promised, in a radio interview with Mike Huckabee, to stick strong to his antiabortion principles.

“I believe there is a cause here, and there is a part of the message that’s missing, and a lot of the people feel left out of the parties," Akin told Huckabee.

It's only fitting that a candidate would take up the antiabortion cause in Missouri: The state has been at the heart of many of the country's most heated abortion battles.

Missouri is the only state that has sent multiple challenges to Roe v. Wade all the way to the Supreme Court - and saw one succeed in affirming state rights to restrict abortion access. Its legislature defunded Planned Parenthood in the early 1990s, years before other states took up a similar cause.

And through the 2000s, Missouri has continued to pass some of the most aggressive abortion restrictions in the country. NARAL Pro-Choice America gives the Show-Me-State an "F" on abortion access.

"I don't think it's correct to say Missouri itself is radically more pro-life than other states," says Cynthia Gornley whose book, Articles of Faith: A Frontline History of the Abortion Wars, focused on Missouri's abortion battles. "What they did have were unbelievably good pro-life organizers and pro-choice people who were quick to take the bait."

Missouri posed one of the first serious tests to Roe v. Wade in 1986, when it passed a law creating numerous restrictions on abortion access. The state disallowed public facilities from being used for abortion and requires doctors to test for a fetus' viability after 24 weeks of gestation. Abortion-rights advocates challenged those restrictions as violating Roe's guarantee of legal access to abortion.

"This was the biggest post-Roe abortion case at that time," Gorney recalls. "There were a lot of people who thought Roe was going to go down."

The Supreme Court did not take down Roe altogether. But in its 1989 ruling, Webster v. Reproductive Health Services, it did affirm states' rights to put limits on abortion access. It allowed the viability testing to continue because it could, as Justice Sandra Day O'Connor wrote for the majority, "promote the State's interest in potential life."

Missouri's local abortion battles have repeatedly exploded into national issues. Its  legislature set its sights on Planned Parenthood in the 1990s, barring the abortion provider from receiving any state funds, according to the Guttmacher Institute's Elizabeth Nash. When a court ruled that regulation unconstitutional, it eliminated its family planning program altogether - years before Texas made a similar move, to much public outcry, in 2011.

The state also pioneered, alongside Nebraska and Virginia, a "partial-birth abortion ban." That law, which outlawed a specific abortion procedure used in late-term cases, passed in Missouri in 1999. Congress took it national in 2003 with the Federal Partial-Birth Abortion Act, which outlawed the procedure in all 50 states.

"It really shows how the Missouri legislature has been hostile and has been that way for many years," says Nash.

Antiabortion legislation has not let up in recent years. Missouri tightened its late-term abortion ban last year to only allow exceptions for cases where the health of the mother is at risk. The legislature followed up this year with a bill barring employers from covering abortion in health insurance plans.

Even with its solid antiabortion record, experts say Missouri is no easy place to advocate for an all-out abortion ban. Akin does still have the solid backing of antiabortion groups, including Missouri Right to Life. That group has applauded his "consistent defense of innocent unborn human life clearly contrasts."

Still, support for abortion bans without exceptions tends to hover around 20 percent of the population. Missouri's Republican establishment, including Sen. Roy Blunt (R-Mo.) and four former senators, have urged Akin to step aside.

"Akin would still retain most of his supporters by focusing on social issues, but McCaskill would be able to make a strong case to women and political independents," says Peverill Squire, a political science professor at the University Of Missouri. " An absolute ban on abortion without any of the usual qualifiers such as rape or a mother's health would make many Republicans uncomfortable."