President Barack Obama promised Democratic lawmakers that the US will continue to keep economic pressure on Iran, keep military options open, and increase missile defense support to Israel if his administration’s nuclear deal with Tehran goes through.

Obama said in a letter addressed to New York Democratic Rep. Jerrold Nadler that if Iran rushes to build a nuclear weapon, “all of the options available to the United States — including the military option — will remain available.”

The president also said the US will uphold sanctions targeting Iran’s non-nuclear activities, such as its support for Lebanon’s Hezbollah group and what Obama calls Iran’s “destabilizing role in Yemen.”

And the letter emphasizes US support for Israel, saying Obama has “consistently viewed Israel’s security as sacrosanct.”

According to the New York Times, Obama “pledged to increase missile defense funding for Israel, accelerate co-development of missile defense systems, and boost tunnel detection and mapping technologies.”

Nadler said he brought up “troubling” questions “about our ability to permanently stop Iran from developing a nuclear bomb, and our commitment to strengthening the US strategic relationship with Israel, as well as Iran’s continued destabilizing influence through support of terrorism and other actions that threaten Israel’s security and the security of our other Middle East allies,” according to the New York Times.

“I am gratified that the president’s response satisfies a number of these concerns,” Nadler said. He remains undecided, however.

Jerrold Nadler (Courtesy)

Jerrold Nadler (Courtesy)

On Thursday, Sen. Claire McCaskill, D-Mo., became the latest to declare her backing for the Iran deal, saying in a statement: “This deal isn’t perfect and no one trusts Iran, but it has become clear to me that the world is united behind this agreement with the exception of the government of Israel.”

McCaskill’s announcement followed a similar declaration a day earlier from Sen. Joe Donnelly, D-Ind., who said: “I am willing to give this agreement the opportunity to succeed.”

Their support brings to 26 the number of Senate Democrats who’ve come out in favor of the agreement aimed at dismantling Iran’s nuclear program in exchange for billions in sanctions relief. Supporters now include 10 of the 12 members on the Democratic side of the Senate Armed Services Committee.

With majority Republicans unanimously opposed, Obama needs 34 Senate Democrats to sustain his veto of a resolution disapproving the deal. The disapproval measure may pass next month. With only two Senate Democrats opposed so far that number is increasingly looking within reach, and supporters could even potentially secure the 41 votes that would block the resolution from passing in the first place.

The dynamic is similar in the House, where Minority Leader Nancy Pelosi told The Associated Press this week that Democrats will back up Obama if he’s forced to veto a disapproval resolution. “We will sustain the veto,” she said. Doing so would require 146 Democrats. The number of publicly declared supporters neared 60 Thursday as Reps. Mike Honda of California and Rosa DeLauro of Connecticut came out in favor, with DeLauro declaring, “The best option for preventing Iran from developing a nuclear weapon is to support the agreement.”

The momentum for the deal signed last month by the US, Iran and five other world powers comes despite GOP anger over a report by The Associated Press on a previously undisclosed side deal between Iran and the UN’s International Atomic Energy Agency. That side agreement would allow Tehran to use its own inspectors to investigate a site it has been accused of using to develop nuclear arms at least a decade ago.