Vice President Joseph Biden shakes hands with lawmakers in the U.S. Capitol in Washington. Biden is to brief the Democrats on the Iran nuclear deal. (Shawn Thew/EPA)

Vice President Biden brought his campaign of personal persuasion to the Capitol for a second straight day Thursday, emerging as the Obama administration’s public salesman to wavering Democrats on the controversial nuclear deal with Iran.

Biden spent 90 minutes huddled in his old office on the Capitol’s first floor with Democrats on the Foreign Relations Committee, making the case that he thinks the deal is the best possible option. Exiting the meeting, Biden acknowledged that the focus of the administration’s pitch now is squarely on congressional Democrats.

“It went well, but they’re all Democrats,” he said in a brief interview.

That’s the early focus of the administration, because the widespread outrage from congressional Republicans since the agreement was announced Tuesday makes it almost certain that the GOP majorities in the House and Senate will deliver majority support for opposing the deal in what are likely to be a pair of mid-September votes.

So, in addition to Thursday’s meeting with Senate Democrats, Biden spent Wednesday morning in a closed-door meeting with the House Democratic caucus, taking many detailed questions from rank-and-file lawmakers with concerns about the plan, particularly regarding Israel’s security.

Speaker of the House John Boehner told reporters the deal struck with Iran over its nuclear weapons building facilities is "wrong for our country." (AP)

The immediate goal is to explain the intricacies of the plan that allows sanctions on Iran to lapse in exchange for limitations on its nuclear program for a decade. The main goal is ensuring that enough Democrats stick with President Obama so that, even if the resolutions disapproving of the deal win majorities, they would pass with less than a two-thirds majority and his veto would be sustained.

Biden’s face-to-face pitch has been personal, explaining his political roots as a strong proponent of Israel during his 36 years in the Senate and his relationship with Obama.

“I’ve been a very supportive vice president; I will always support the president, but my deal with him from the very start was: I will always support you, but I’m not going to sell if I don’t agree with it; don’t ask me to come sell something if I don’t agree with it,” Biden told Democrats Thursday, according to Sen. Timothy M. Kaine (D-Va.).

According to Kaine, the vice president reminded the senators of his previous role as chairman of their committee, helping negotiate arms treaties.

“I’m here and I’m selling, because I agree with this,” Biden said.

With a dozen or more Democrats, along with 54 Republicans, expressing doubts about the deal, the Senate vote could get perilously close to the 67 votes needed to override a veto from Obama. The administrationdrew bipartisan criticism from its announcement that it would seek a U.N. vote of support next week, well ahead of the congressional schedule for consideration. Liberals such as Sen. Chris Murphy (D-Conn.) and conservatives such as Sen. Bob Corker (R-Tenn.) expressed problems with that timing.

“I look at that as an affront to the American people,” Corker told reporters at a news conference outside the meeting Biden held with Democrats.

The current procedure for handling the Iran deal materialized earlier in the spring when Kaine worked with Republicans to come up with a congressional review that will give the House and Senate as many as 60 days to consider the pact.

During that time the president can lift only sanctions that were imposed by the executive branch, leaving in place those sanctions against Iran that previous Congresses imposed.

Many officials in the administration are flooding Democrats with information, working the phones and planning meetings. A group of Jewish Democrats received a classified briefing from Ben Rhodes, deputy national security adviser, on Thursday. Kaine got a call early Tuesday, as the deal was being unveiled, from Antony Blinken, the deputy secretary of state.

Next week three secretaries — John F. Kerry of State, Ernest Moniz of Energy and Jack Lew of Treasury — will be on Capitol Hill for briefings in the House and Senate.

For this week, however, Biden was the main pitchman for the deal to Democrats.

His ties to the Senate are legendary, but his connection to House Democrats is possibly even stronger. Over the last seven years Biden has tended to dozens of fundraisers for rank-and-file Democrats and made campaign stops in their districts, while Obama has generally appeared only at events for himself or fundraisers for congressional campaign committees.

Similar to his pitch to Senate Democrats, Biden spoke very little at the beginning of his session with House Democrats and instead let them ask as many questions as they could. The session paid a big dividend when House Minority Leader Nancy Pelosi (D-Calif.) announced Thursday morning that she would support the Iran deal and that she would aggressively lobby fellow Democrats to back the president.

“He was spectacular,” Pelosi said of Biden.

Of the 188 House Democrats, Pelosi will need to persuade about 145 of them to vote with the president on the Iran deal.