Robert Menendez, a Democrat representing New Jersey in the Senate, chairs the Foreign Relations Committee. Lindsey Graham, a Republican representing South Carolina in the Senate, is a senior member of the Armed Services Committee.

The new face of Iran we anticipated seeing at the United Nations last week sounded and looked quite similar to the old face of Iran we have come to know.

We expected a charm offensive. We readied ourselves for a possible diplomatic breakthrough. But we were left underwhelmed.

For weeks now, we have followed the rhetoric originating from Iran. We had been cautiously hopeful.

As proponents of a series of bipartisan bills legislating sanctions targeting Iran’s oil and banking industries and lawmakers who have worked with our European allies to isolate Iran from international financial markets, we understand full well the result of crippling sanctions.

Iran expressed an interest in negotiations because the economic pain levied on it by Congress and the international community has become unbearable. This outreach was borne out of necessity, not a sudden gesture of goodwill.

For Ayatollah Ali Khamenei to tell commanders of the Islamic Revolutionary Guard Corps that Iran would pursue a diplomatic course of “heroic flexibility” was significant, even a breakthrough.

When Hassan Rouhani campaigned and resoundingly won a presidential election on a platform of “prudence and hope,” then penned an op-ed in this paper headlined “Time to engage; Iran’s new approach to the world” days before traveling to the U.N. General Assembly, we had reason for guarded optimism.

The sanctions efforts we support in Congress, alongside the four U.N. Security Council resolutions criticizing Iran’s nuclear program and applying multilateral sanctions against the regime, seek to impel Iran to walk itself back from the nuclear precipice.

We remain skeptical about Tehran’s intentions. Iranian leaders are skilled negotiators with expertise in delay tactics and obfuscation.

Yet to ignore the overtures coming from Iran during this period of furious public diplomacy would have been imprudent, especially when a peaceful resolution preventing Iran from achieving nuclear capability is the outcome we all aspire to achieve.

But what happens in Tehran seems to stay in Tehran, and President Rouhani’s charm offensive didn’t quite follow him to New York. Rouhani was betwixt and between, reaching out to our world, but still shackled by his world. He spoke of tolerance and responsibility during his General Assembly speech, while listing grievances against the West and launching into a diatribe against Israel — a familiar refrain we’ve heard before. Rouhani’s inability to reciprocate to President Obama’s offer of a handshake at the United Nations was weak, yet Rouhani accepted Obama’s phone call on Friday.

As Rouhani returns home, diplomacy remains our hope and goal. But our resolve to prevent Iran from achieving a nuclear weapons capability remains unchanged.

We believe that four strategic elements are necessary to achieve a resolution of this issue: an explicit and continuing message that the United States will not allow Iran to acquire a nuclear weapons capability, a sincere demonstration of openness to negotiations by Iran, the maintenance and toughening of sanctions and a convincing threat of the use of force.

The national security implications of a nuclear Iran are unimaginable — threatening the very existence of our ally Israel, as well as launching an all-but-certain nuclear arms race in the world’s most volatile region. Diplomacy is our hope, but the U.S. resolve to take whatever action is necessary to prevent Iran from becoming a nuclear state will not be compromised.

In the coming days, we will be outspoken in our support for furthering sanctions against Iran, requiring countries to again reduce their purchases of Iranian petroleum and imposing further prohibitions on strategic sectors of the Iranian economy.

We proceed with an open hand, but there can be a deal only when Iran’s actions align with its rhetoric.