(CNN) — Rick Santorum launched a drive against the nomination of former Republican Senator Chuck Hagel as defense secretary on Wednesday.
Santorum, the former senator from Pennsylvania and 2012 GOP presidential candidate, announced his opposition to President Barack Obama's Monday announcement that he's nominating Hagel to succeed retiring Defense Secretary Leon Panetta.
John Brabender, a top political adviser to Santorum, tells CNN that Patriot Voices, the pro-Santorum run 501(c)4 advocacy group, will go up with online ads opposing the nomination.
Santorum, who served with Hagel in the Senate for 10 years and who was a member of the Armed Services Committee, opposes the nomination because of Hagel's positions on Iran and Israel, according to Brabender.
Meanwhile, Hagel spent his second day of meetings at the Pentagon trying to set his record on Iran straight.
He said he supports tough international sanctions against Iran, in an attempt to counter complaints by critics who say he favored talking directly with the government in Tehran, according to defense officials with direct knowledge of the nominee's conversations Wednesday.
Hagel told Pentagon staff he also believes all options in dealing with Iran's nuclear program should be on the table, including military action, according to the officials.
The nominee has begun meeting with defense staff as he prepares for his confirmation hearing, which is expected in late January or early February, though no specific date has been chosen, according to a Senate staffer.
The official said Hagel wanted to set the record straight and that he believes he has been misrepresented by his critics.
The messaging is "part of a bigger effort, he's also been reaching out to the Jewish community on their concerns...he's making the appropriate rounds," according to the official.
Hagel also has drawn criticism from both Republicans and Democrats for his perceived lack of support for Israel. The former senator from Nebraska pushed back earlier this week, telling the Lincoln Journal Star that there is "not one shred of evidence that I'm anti-Israeli, not one (Senate) vote that matters that hurt Israel."
Republicans are critical of Hagel for opposition to the 2007 surge of U.S. forces in the war in Iraq, and of his opposition to unilateral sanctions against Iran over its nuclear weapons program.
"I have not supported unilateral sanctions because when it is us alone, they don't work and they just isolate the United States," Hagel has said.
Santorum, once a long shot in the 2012 race for the Republican presidential nomination, came out on top in the Iowa caucuses and battled eventual nominee Mitt Romney deep into the primary calendar before suspending his bid. Santorum is seriously considering another run for the White House in 2016.
"I'm open to that possibility," said Santorum when asked on CNN's "Piers Morgan Tonight" in November about another run.