In his State of the Union address Tuesday night, President Obama delivered a strong defense of his administration’s on-going diplomacy with Iran and a threat to those in Congress who could wreck what progress has been made so far.

“The sanctions that we put in place helped make this opportunity possible,” Obama said. “But let me be clear: If this Congress sends me a new sanctions bill now that threatens to derail these talks, I will veto it. For the sake of our national security, we must give diplomacy a chance to succeed.”

We believe that the recent diplomatic efforts of the international community are a positive step toward a reduction in Iran’s capacity to build nuclear weapons and a thawing of the Islamic republic’s hostile relationship with the West. While these diplomatic efforts have been modest so far, Obama is right to discourage those in Congress threatening to pass new economic sanctions against Iran that could kill the prospects of future negotiations.

The deal struck in November between Iran and the “P5-plus-1” powers — the United States, Britain, France, Russia, China, and Germany — requires Iran to somewhat scale back its nuclear enrichment and uranium stockpiles and to not install new centrifuges in exchange for a slight relaxation of economic sanctions. Most importantly, the deal is contingent on the West agreeing to impose no further sanctions as long as Iran is complies with the deal.

It is too soon to know the degree to which Iran will be willing to comply with these diplomatic efforts, but the early indications are promising. On Wednesday, inspectors from the International Atomic Energy Agency visited an Iranian uranium mine for the first time in a decade. It’s a small step, but it’s certainly a positive development.

Unfortunately, despite such early indications of compliance, many members of Congress support new sanctions on Iran. Fifty-nine senators, including some Democrats, have cosponsored a bill that would install new sanctions if no permanent deal with Iran can be reached. The Iranians, seeing such a bill as a violation of the terms of their preliminary agreement, have threatened to cease negotiations if it becomes law.

Those who support the Senate plan argue that it is merely an insurance policy in the case that negotiations break down.

“The … bill is an insurance policy against Iran’s development of nuclear weapons and ensures a process for the peaceful dismantlement of Iran’s nuclear infrastructure,” Sen. Mark Kirk, R-Ill., one of the bill’s cosponsors, said in a statement after Obama’s speech.

Even though Obama has promised to veto any additional sanctions passed by Congress, the apparent willingness on the part of our lawmakers to undermine the first meaningful negotiations with Iran in years is appalling. By all accounts, the existing sanctions caused enough economic disruption in Iran to bring it to the negotiating table. It seems as though those sanctions worked exactly as they were intended; why endanger that progress with even more punishing sanctions?

Obviously, a nuclear-armed Iran represents a serious threat to the United States and Israel, but that threat is not sufficient to abandon fledgling diplomacy in favor of outright hawkishness. In response to their overture of cooperation, the Iranians deserve our cooperation — at least until they prove otherwise.