President Obama during a stop at Charmington's Cafe in Baltimore on Thursday. (AP Photo/Evan Vucci)

President Obama used a closed-door meeting with Democratic senators Thursday to once again threaten to veto a bill ordering stiffer sanctions against Iran -- and, in legacy mode, repeatedly vowed to former colleagues he would remain "on offense" against the GOP Congress on a range of issues.

Meeting in Baltimore at a downtown Hilton Hotel across from Camden Yards, Obama defended his decision to use his executive powers to change the nation's immigration laws and reestablish diplomatic ties with Cuba, according to several people in attendance. He also said he would veto a bill to impose stiffer sanctions on the Iranian regime, reiterating similar statements he and administration officials have made publicly.

Obama's decision to reiterate the threat face-to-face is notable because the proposal enjoys significant support from Democrats, especially one of its lead authors, Sen. Robert Menendez (N.J.).

According to people who attended the meeting, Obama addressed the issue during a question-and-answer period and was clearly prepared to deal with the inquiry. The question came from Menendez and prompted a brief exchange between them as they both expressed disagreement with one another.

Obama "was very firm and so was Menendez but it was not heated or contentious," said one attendee, granted anonymity to discuss a meeting that Democrats agreed wouldn't be discussed publicly.

"He was fairly unequivocal," said another attendee.

Members of both parties agree that Iran should suffer stronger sanctions for its continued work to develop its nuclear program and see passage of the sanctions bill as an early opportunity for both parties to demonstrate bipartisan cooperation in the new Congress.

But Obama has resisted the bill as talks continue between his administration and Iranian officials on the country's nuclear ambitions. Obama and Secretary of State John F. Kerry recently announced plans to extend the talks for a few more months.

The disagreement also exposes a growing difference of opinion between the White House and Menendez -- technically the caucus's leading voice in foreign affairs because he is ranking Democrat on the Senate Foreign Relations Committee. Menendez, who is Cuban American, has also denounced Obama's decision to reopen ties to Cuba and is expected to join Republicans in blocking funding for a new Havana embassy and the nomination of a new U.S. ambassador to the country.

During his hour-long meeting with senators, Obama otherwise didn't share anything terribly new, according to several attendees. He didn't use the meeting to share any specific plans for his State of the Union address next Tuesday and only broadly discussed the nation's improving economy and the ongoing debate over immigration with Republicans.

Repeatedly, Obama vowed to remain "on offense," said another attendee.

He was "very positive and upbeat. The president’s plainly looking to his legacy and his place in history, not the immediate poll numbers. He gave a very strong, cogent case for his using executive actions," said the person, who also wasn't authorized to discuss the meeting.

Earlier, Obama had lunch at a Baltimore cafe with Sen. Barbara Mikulski (D-Md.), a lifelong Baltimore resident, and three other women invited by the White House to join them. The president said the group discussed his plans to provide more paid sick leave to federal employees with new children as part of his push to get Congress to broaden the range of benefits for feds in hopes of attracting new talent.