"A lot of these anti-choice politicians don't run on the issue," Keenan said in an interview Tuesday with The Associated Press. "They run on jobs, or they run on the economy. And then they show up in these state legislatures, and they begin to advance very anti-choice legislation."
In the four decades since Roe v. Wade, a series of court decisions have narrowed its scope. With each decision, lawmakers in multiple states have followed up by making abortions more difficult to obtain or imposing restrictions on providers.
According to the New York-based Guttmacher Institute, a reproductive-rights think tank, 135 laws aimed in some way at restricting access to abortion were enacted in 30 states in 2011 and 2012. More such measures already have been proposed in several states this year.
Kansans for Life, the most influential abortion group lobbying state lawmakers in Topeka, eschews proposals designed to set up a head-on legal challenge to the Roe v. Wade decision, fearing the Supreme Court might wipe out some of the gains achieved by abortion opponents in recent years.
"We'd like to continue on our successful strategy," Kathy Ostrowski, the group's legislative director, said during a pre-rally news conference. "We feel that we're making better strides that way."
Tuesday's events won't be the only anniversary observances. The annual March for Life, which traditionally draws several hundred thousand abortion opponents to Washington, is scheduled for Friday.
Although bills to strengthen access to abortion are rare, there are some pending proposals in New York and Washington state.
In their state of the state speeches this month, New York Gov. Andrew Cuomo endorsed a bill that would further entrench the right to abortion while Washington's new governor, Jay Inslee, said he wants to enact a measure that would require insurers who cover maternity care - which Washington insurers are mandated to provide - to also pay for abortions.
Both Cuomo and Inslee are Democrats.
"Forty years ago, the United States stood as an example to the rest of the world in recognizing a woman's right to a safe and legal abortion as a constitutionally protected right," said Nancy Northup, president and CEO of the Center for Reproductive Rights. "But the women in this country shouldn't have to rely on the courts to right the wrongs of their elected officials."