Sen. Robert Menendez Robert (Bob) MenendezKasie Hunt to host lead-in show for MSNBC's 'Morning Joe' Senators ask for removal of tariffs on EU food, wine, spirits: report VOA visa decision could hobble Venezuela coverage MORE's (N.J.) decision to step aside temporarily as ranking Democrat on the Senate Foreign Relations Committee following his indictment on Wednesday could jeopardize Congress's chances of passing Iran legislation.

Menendez has co-authored legislation with Chairman Bob Corker Robert (Bob) Phillips CorkerHas Congress captured Russia policy? Tennessee primary battle turns nasty for Republicans Cheney clashes with Trump MORE (R-Tenn.) that would allow the Senate to weigh in on any nuclear deal with Iran, and a separate bill that would restore and impose tougher sanctions on Iran if it walks away from talks or violates a deal.

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The Foreign Relations Committee is set to vote April 14 on the bill he co-authored with Corker calling for Senate review of an Iran deal. If Menendez is out of the picture long-term, it could sap Democratic support for legislation that the White House has already threatened to veto.

Typically, the most senior Democrat on a committee steps in when a member takes leave from a post, but Minority Leader Harry Reid Harry Mason ReidGraham signals support for confirming a Supreme Court nominee this year Trump signals he will move to replace Ginsburg 'without delay' Senate Republicans signal openness to working with Biden MORE (D-Nev.) would make the final decision.

Corker said in a statement to The Hill that he had "no knowledge of the judicial matters at hand" but said he expects Menendez "will continue to play a constructive role" on his panel.

After Menendez, the next most senior Democrat on the committee is Sen. Barbara Boxer Barbara Levy BoxerThe Hill's Morning Report - Presented by Facebook - Biden, Harris launch Trump offensive in first joint appearance Bottom line Polls show big bounce to Biden ahead of Super Tuesday MORE (D-Calif.), an ally of President Obama who opposes passing any Iran legislation before the final June 30 deadline in the talks.

She has introduced competing and less stringent legislation with six other Democrats that calls for the White House to regularly report on Iran's compliance with any deal, and sets up an expedited process for Congress to reinstate sanctions if Iran violates an accord.

However, Boxer is not running for reelection in 2016 and is already the ranking Democrat on another panel.

That means the job would likely fall to Sen. Ben Cardin Benjamin (Ben) Louis CardinPPP application window closes after coronavirus talks deadlock Congress eyes tighter restrictions on next round of small business help Senate passes extension of application deadline for PPP small-business loans MORE (D-Md.), who was a co-sponsor of the original bill authored by Sens. Mark Kirk Mark Steven KirkLiberal veterans group urges Biden to name Duckworth VP On the Trail: Senate GOP hopefuls tie themselves to Trump Biden campaign releases video to explain 'what really happened in Ukraine' MORE (R-Ill.) and Menendez that would restore and impose tougher sanctions on Iran.

Cardin also signed a letter to the president saying he would wait until after the end of March to support that bill, and has indicated he would support Corker-Menendez.

After Cardin, Sen. Jeanne Shaheen Cynthia (Jeanne) Jeanne ShaheenSenate Democrats introduce bill to sanction Russians over Taliban bounties Trump-backed candidate wins NH GOP Senate primary to take on Shaheen Democratic senator urges Trump to respond to Russian aggression MORE (D-N.H.) would be the next most senior member. She has typically leaned somewhat hawkish on foreign policy. However, she did not co-sponsor the original version of Kirk-Menendez, and criticized an open letter to Iran by Republicans warning it that any deal might not last past the Obama administration.

Sen. Chris Coons Christopher (Chris) Andrew CoonsBiden promises Democratic senators help in battleground states Shakespeare Theatre Company goes virtual for 'Will on the Hill...or Won't They?' The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep MORE (D-Del.), next after Shaheen, is a co-sponsor of the original Kirk-Menendez sanctions bill, a co-sponsor of the latest version and has also signed the letter saying he would support it after March.

All Senate Democrats last week voted to unanimously pass a nonbinding budget amendment in support of sanctions if the administration could not certify to members of Congress that Iran was not violating any deal.

Last updated at 8:46 p.m.

— Jordain Carney contributed.