Sens. Joe Manchin (D-W. Va.) and Kyrsten Sinema (D-Ariz.) are privately advising the nine House centrist lawmakers trying to force Speaker Nancy Pelosi to hold a quick vote on a bipartisan infrastructure deal, lawmakers and aides tell Axios.

Why it matters: The two moderates who've stirred the biggest frustrations and held the most sway in their party over the infrastructure negotiations are helping allies in the House to stake out — and defend — their centrist position.

• They're offering encouragement and advice on how to negotiate with the White House and congressional leadership.
• Their behind-the-scenes support also indicates the degree to which Manchin and Sinema have prioritized getting the $1.2 trillion bipartisan infrastructure deal to final passage and in front of Biden for his signature.

The big picture: The conversations are bolstering House centrists' resolve. Since publicly demanding last Friday that Pelosi first bring the infrastructure bill to the floor before considering a larger package through a $3.5 trillion budget plan, the nine lawmakers have been subject to a combination of private scorn and public pressure.

• Pelosi referred to their tactics as “amateur hour” in a leadership call earlier this week, Politico reports.
• On Tuesday, the White House released a statement endorsing Pelosi’s approach, expressing “hope that every Democratic member supports this effort to advance these important legislative actions.” Pelosi quoted from that statement in a “Dear Colleague” letter she sent to reiterate her position.
• Brian Deese, director of the National Economic Council, and Louisa Terrell, the head of legislative affairs, Shuwanza Goff, the House liaison, as well as Energy Secretary Jennifer Granholm, have been contacting lawmakers, urging them to vote for the rule.
• So far, the nine lawmakers are withstanding pressure and remain committed to their strategy.

Between the lines: Both Manchin and Sinema have longstanding relationships with some of the centrist lawmakers including members of the "Problem Solvers" who worked together on COVID-19 relief bills in 2020.

Go deeper: The nonpartisan group "No Labels" is launching a six-figure ad by on national cable to give some air cover to the nine lawmakers.

• "This unbreakable nine is showing America that we can still do amazing things," says the ad's narrator.

What we're hearing: One possible way out of the standoff is for Pelosi to promise the centrists a vote on the infrastructure deal by the end of September.

• That could give them assurances their infrastructure bill would receive a vote without having to wait for the Senate to decide on specifics of the $3.5 trillion bill that are far from complete.