The press conference comes less than a week before Iowa's traditionally conservative Republican voters head to caucus sites and the same day a group of an anti-abortion leaders urged Iowans to oppose Trump's candidacy, suggesting inconsistencies on the issue.
"All I can tell you is this I'm pro-life and I've been pro-life a long time," Trump said Tuesday.
But Trump said in 1999 that while he hated the "concept of abortion" he was "pro-choice." On the 2016 campaign trail, Trump has positioned himself as an opponent of legalized abortion.
Asked what penalties he would support for women who undergo abortions or doctors who perform them, Trump demurred.
"I just don't want to talk about that right now. Everybody knows my views and I think my views are very plain," Trump said.
Addressing supporters following the press conference, Trump conceded that his views on abortion have changed and noted that when he was just a businessman he "never gave it much thought."
"When it comes to pro-life I've evolved," Trump said.
Asked by reporters whether he considers Plan B, the morning after pill, to be the same as an abortion, Trump again would not divulge his position.
Instead, Trump touted a recent endorsement from prominent evangelical leader Jerry Falwell, Jr., the president of the evangelical Liberty University and son of its founder, and pointed to poll numbers showing him ahead of Texas Sen. Ted Cruz in support from evangelical voters in Iowa.
Cruz has spent recent weeks questioning Trump's conservative credentials and suggesting that Trump's "New York values" are not aligned with the conservative views of Iowan Republican primary voters.
Trump fired back as he has in recent days, calling Cruz "really a nasty person."
"I question Ted Cruz. I question him very (strongly)," Trump said when asked about Cruz challenging Trump's values.
Sen. Ben Sasse, a Nebraska Republican who will join Cruz and Sen. Marco Rubio on the campaign trail in Iowa this week, also asked this week whether Trump had repented for his marital infidelities.
"I think everybody knows about me," Trump said simply, adding later that bringing that up was a "cheap shot."
Flanked by Maricopa County Sherriff Joe Arpaio, who gained notoriety for his hardline policies aimed at undocumented immigrants, Trump did offer some additional details on his pledge to build a wall on the U.S.'s southern border and deport all undocumented immigrants living in the United States.
Trump first said he would "get Congress's approval" before implementing those policies, before adding that he "would at least speak to Congress."
Trump also touted his plan to deal with illegal immigration as the "toughest" of the presidential candidates.
During the press conference, Trump also announced he was likely to skip Thursday's GOP debate due
to a deepening fight with the Fox News Channel.
Afterward, Trump's campaign manager Corey Lewandowski said Trump's decision on the debate was final.
"Mr. Trump will not be participating in the Fox News debate on Thursday night. It's not under negotiation," he said.