WASHINGTON -- Let the congressional sales pitch of the Iran deal begin. Vice President Joe Biden will meet with House Democrats on Wednesday to brief them on the Iran nuclear deal. The meeting comes only a day after President Barack Obama announced that a deal had been struck between the United States, Iran and several European nations.

House Democrats will be key to ensuring that Obama’s deal isn't canceled by congressional Republicans, who are likely going to seek to reverse the agreement. Because it is an “executive agreement” and not a treaty, congressional approval isn’t required but could be use to destroy the deal.

Under legislation passed in May, Congress will vote either to approve or disapprove the Iran deal after a 60-day review. It is widely expected that Republican leadership will move legislation to disapprove of the deal, which will then be vetoed by Obama. The administration will then need enough Democrats to hold together to block a veto override.

The key to blocking the veto override is likely to be House Minority Leader Nancy Pelosi. She has proven to be one of the most effective whips in modern congressional history and has delivered the needed votes at important times for the president -- or in a handful of cases against Obama.

GettyImages-480086390 House Minority Leader Rep. Nancy Pelosi, D-CA, is likely to be key to ensuring President Barack Obama's Iran deal isn't scuttled by the U.S. Congress. Pictured, Pelosi speaks during a news conference on July 9, 2015 on Capitol Hill in Washington, DC. Photo: Getty Images/Alex Wong

Pelosi likely will need to get 146 of the 188 Democrats currently serving in the House -- minus a few if they pick up a couple of moderate Republicans in competitive districts. For progressives, it’s likely to be an easy vote. But for Democrats in competitive districts, it could take a lot of convincing to get them to stay with the president.

Biden’s meeting comes at the request of Pelosi. It is described, in an invitation to Democratic members to attend, as the first in a series of meetings that will be held about the deal.

Biden’s visit will also come one day after Hillary Clinton met with House Democrats in the same room. Clinton was there as part of an outreach to build her 2016 campaign and talked about her views and policy issues. Speculation continues to swirl as to whether Biden will challenge Clinton for the nomination.