Sen. Tom Cotton (R-Ark.). (AP Photo/Danny Johnston)

The controversy over the GOP letter to Iran continues to rage this morning, with the letter’s chief sponsor — Sen. Tom Cotton of Arkansas — taking to Morning Joe to defend the missive. Democrats have attacked the letter — which advises Iranian leaders that any agreement on that country’s nuclear program needs Senate approval and can be undone by a future president — as an unprecedented effort to undermine a sitting president’s foreign policy negotiations.  Cotton is digging in, insisting the Senate must vote on any nuclear deal.

On this, I’m with Jonathan Bernstein: I’m of two minds about the underlying substance of the letter. I would like to see Congress more involved in making foreign policy, but the letter’s tone and apparent goal of undermining the president during international negotiations do seem deliberately inflammatory and destructive. Indeed, even Republicans are charging it over-reached.

Politico reports that several Republican Senators are now saying the letter from many of their GOP colleagues to Iran’s leaders could backfire by injecting partisanship into the argument over Iran and making it less likely that Democrats support a drive to restrict the administration’s efforts to reach a nuclear deal with Iran.

There are two bills being considered — one that would require a Congressional vote to approve or reject a final deal; and the other that would impose new sanctions, perhaps scuttling any such deal before diplomacy has a chance to work. Senator Bob Corker tells Politico the letter it could imperil his goal of amassing a veto-proof Senate majority in favor of legislation requiring Congress to approve the deal. The Wall Street Journal editorial page also attacks Cotton’s letter this morning for the same reason, arguing that it’s a “distraction” from the goal of getting enough Dems to support that legislation to override a veto, by giving Obama a way “to charge that Republicans are playing politics.”

Two points about this. First, it’s probably true the letter will make it easier for wavering Democrats to side with the administration on Iran. But if that is right, it’s really too bad it requires something as provocative as this to make Democrats feel “safe” in arguing for giving diplomacy a chance to work. Polls have shown solid majority support for the general idea of lifting sanctions in exchange for Iran restricting its nuke program, yet some Dems still act as if they can’t win this argument on the merits in the eyes of the public, and need an “assist” from GOP overreach (such as the recent GOP invitation, with no consultation with Obama, to Benjamin Netanyahu to address Congress, or, now, this new Cotton adventure).

Which brings us to the second point: Hillary Clinton is very likely going to be asked about the Cotton letter one of these days, and we could now see this whole fracas spill over into the 2016 presidential race. This quote from Cotton is noteworthy:

“We already have four senators on the letter who were thinking about running for president,” said Cotton, who later added: “I’ve spoken privately with other presidential candidates who might join us.”

GOP presidential hopefuls like Ted Cruz and Marco Rubio are on the letter, and it seems likely Cotton means he has “spoken privately” with the likes of Scott Walker and Jeb Bush, and that they have signaled their support. So one imagines they will be asked about this one of these days. Given that Cotton’s letter reads as if its intended audience was not just the Iranian leadership, but the GOP base as well, you’d think Walker and Bush will eagerly voice their support.

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* DOES OBAMA HAVE POWER TO MAKE DEAL WITH IRAN? The underlying dispute here is over whether Obama has the legal authority to reach a temporary deal with Iran and other world powers without Senate approval, and the Wall Street Journal has a good explainer, concluding that there are no easy answers to this question:

Treaties are binding…But the White House has made clear it will instead seek an executive agreement, or something like it. This approach will draw heat from Congress, and legal experts will watch the proceedings closely to see the constitutional implications.

As one expert puts it, the GOP argument “isn’t that the president can’t make executive agreements. But, rather, that the president can’t make an executive agreement on an issue of this importance.”

* OBAMA WAR AUTHORIZATION REQUEST HITS A WALL: Shocking, but true. National Journal reports that Congress is unlikely to support Obama’s request for authorization for the war on ISIS, and is unlikely to pass its own version of any such authorization:

The problem: The Obama administration believes it already has the authority it needs to carry out its mission, and absent any sense of urgency in Washington, there’s scant political pressure to build a coalition for a tough war vote. On the Senate side, Foreign Relations Committee Chairman Bob Corker has warned that the administration’s proposal is already in trouble, with little buy-in from Democrats. And while liberals are leery of any vote that would put them on the record for another war, conservative hawks have criticized the AUMF for being overly restrictive.

As I’ve noted before, this whole thing is mostly a charade to begin with, so Democrats may as well stick to their demand for meaningful restrictions on Obama’s war-making authority, even if it means nothing passes in the end.

 * HILLARY PREPARING TO ADDRESS EMAIL MESS: Politico’s Glenn Thrush and Josh Gerstein report:

Hillary Rodham Clinton is likely to hold a press conference in New York in the next several days to answer reporters questions about a controversy surrounding her use of a private email account at the State Department, according to three people close to the potential Democratic frontrunner.

Good. There are plenty of questions that remain unanswered, and while calling for state to release 55,000 pages of emails is a good first step, the occasional tweet won’t cut it.

 * DEMS WORRY ABOUT HILLARY EMAIL MESS: Emily Schultheis reports that Democratic donors and activists are increasingly worried about the email controversy:

Party operatives and strategists are welcoming the first signals they’ve seen from Clinton World, saying Clinton must speak publicly about these controversies if she intends to reclaim the news cycle before her expected campaign launch in April. Equally important, Clinton needs to calm the fears of Democratic supporters and donors who might be getting skittish about the strength of her campaign. But Democrats acknowledge that while her actions will help, this planned press conference will not be the end of questions about her actions and motivations. In other words, even Clinton’s supporters realize the story isn’t going away.

No, it probably isn’t.

* HILLARY, JEB BUSH SEEN AS CANDIDATES OF PAST: A new NBC News/Wall Street Journal poll finds that Hillary Clinton and Jeb Bush share an unenviable attribute: Majorities of the American people think both would represent a return to the policies of the past. Americans say that about Bush by 60-27; and about Clinton by 51-44. Scott Walker supporters might understandably seize on this to amplify his argument that only a (relatively) fresh GOP face can beat Clinton.

* AND THREE REASONS DEMS WORRY ABOUT HILLARY: NPR has a good rundown. This is probably the most important one: “There’s no Plan B.” No, there isn’t.