(CNN) - The dinner at Vice President Joe Biden's home Sunday night with Republican senators–which lasted from 7 p.m. to 10 p.m. ET–was "serious and thoughtful," with discussions revolving around not only the unintended consequences of military strikes, but also the effectiveness of what the president intends to do, according to a source with knowledge of the dinner.
Biden told the dinner participants that the president had never been to the vice presidential residence before Sunday night, the source told CNN.
The president stayed at the dinner until about 8:15 p.m. ET.
Questions were also raised about why not wait for the United Nations report if a strike is not as time-sensitive as the White House claims. The extent of Russian outreach was also a topic of discussion.
In addition, questions were raised about the language of the Sen. John McCain's amendment, which was added to the bill passed by the Senate Foreign Relations Committee last week. That amendment by the Republican senator from Arizona said it is "the policy of the United States to change the momentum on the battlefield in Syria." For some, that signaled more involvement in a civil war that no one wants to get involved in.
As for intelligence, this source made the case that those who have been privy to much of it have "no doubt" that the "regime was involved in the strikes." This source described it as the "delegated authority" of Syrian President Bashar al-Assad, meaning it could have been any number of those involved in the chain of command, including his brother, generals, those who deal with chemical weapons, etc.
"It's murky who gave the exact order," the source said. "But it is not murky that it comes from the regime."
It also seems, from another source familiar with the vote counting, that the White House is going for what counts as a big vote these days–more than 61 in the Senate.
The question, another source added, is what would happen next. If the Senate was to approve the measure, and the House vote still looked a 'nay,' would the White House strike?
According to the White House, the guest list included Sen. Lindsey Graham of South Carolina; Sen. Susan Collins of Maine, Sen. Saxby Chambliss of Georgia, Sen. Bob Corker of Tennessee, Sen. Kelly Ayotte of New Hampshire and Sen. Deb Fischer of Nebraska.