A key annual defense bill is poised to serve as a battleground over President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE’s nuclear weapons policy.

On issues ranging from the size of the U.S. nuclear arsenal to whether to leave open the possibility of launching a nuclear first strike, leading Democrats in the House and Republicans in the Senate have been meticulously laying out their cases. Those debates will come to a head soon, as the Senate Armed Services Committee begins to consider its version of the defense policy bill in two weeks.

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“I think there’s tremendous support on the Senate side for the triad,” said Sen. Deb Fischer Debra (Deb) Strobel FischerHillicon Valley: Election officials prepare for new Russian interference battle | 'Markeyverse' of online fans helps take down a Kennedy | GOP senators unveil bill to update tech liability protections Google, Apple, eBay to meet virtually with lawmakers for tech group's annual fly-in Congress botched the CFPB's leadership — here's how to fix it MORE (R-Okla.), the chairwoman of the subcommittee in charge of nuclear weapons, referring to the three methods of delivering a nuclear weapon. “I think everybody’s well aware of the importance that we make sure all three legs are strong.”

The Trump administration’s nuclear posture review, released February 2018, largely follows the Obama administration’s nuclear modernization plans, but also calls for new weapons such as a so-called low-yield warhead and a new sea-launched cruise missile.

The Congressional Budget Office has estimated modernizing the nuclear arsenal will cost more than $1 trillion over the next 30 years.

House Armed Services Committee Chairman Adam Smith David (Adam) Adam SmithWhen 'Buy American' and common sense collide Overnight Defense: Marine Corps brushes off criticism of Marines' appearance in GOP convention video | US troops injured in collision with Russian vehicle in Syria | Dems ask for probe of Vindman retaliation allegations Democrats press Pentagon watchdog to probe allegations of retaliation against Vindman brothers MORE (D-Wash.), who has long lambasted the price tag for nuclear modernization, pledged to make the issue a priority when he took control of the gavel after Democrats won back the House.

One of the first hearings Smith held as chairman was on outside experts’ views on U.S. nuclear policy, and two of his major public addresses since the midterm elections have been at nuclear conferences.

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In the hearing and speeches, he questioned the need for the nuclear triad, said he wants to “kill” the low-yield warhead and blasted Trump for casting aside nuclear treaties.

In late January, Smith also re-introduced his “No First Use Act” — with backing from presidential candidate Sen. Elizabeth Warren Elizabeth WarrenDimon: Wealth tax 'almost impossible to do' CNN's Don Lemon: 'Blow up the entire system' remark taken out of context Democrats shoot down talk of expanding Supreme Court MORE (D-Mass.) — that would make it U.S. policy not to strike first with nuclear weapons.

Smith told The Hill this week he is not yet sure what exactly he’ll put in his version of the National Defense Authorization Act (NDAA), saying he is still getting a feel for where his members are on the issue.

His committee isn’t scheduled to begin considering the bill until June. Generally, he said, he is eying three areas to address: new weapons such the low-yield warhead, the triad and nuclear dialogue with Russia and China.

“We’re still in that laying out the case mode,” he said. “My overarching goal here is to try to make nuclear war less likely. And there’s a lot of different pieces to it, but awareness that we’re stumbling into another nuclear arms race, trying to figure out what we can do to increase dialogue with Russia and China and renew arms control discussions so we don’t put ourselves in that positions — all of those things are part of it.”

One thing Smith did say is likely to be in the bill is language supporting the New START Treaty, which caps the number of deployed nuclear warheads allowed to the United States and Russia. The treaty is up for extension in 2021, and Trump has indicated he wants China to join the pact as a condition for renewal — something supporters of the treaty describe as a “poison pill.”

“I think we’ll probably have some statement on New START, an expression that we need to stay in it,” Smith said. “If we need to update it fine, but let’s not abandon arms control discussions.”

At the nuclear hearing, Smith said he did not think intercontinental ballistic missiles — the ground component of the triad — are necessary for U.S. nuclear deterrence because of the air and sea components.

Smith later walked the comment back, saying at one of his speeches he wasn’t sure if the best approach to reduce the size of the arsenal is to eliminate a leg of the triad or cut the number of warheads from each, but not before he got fierce backlash from Senate Republicans.

Fischer issued a statement in March saying Smith’s comments were “dangerous" and "misguided.”

Asked this week if she thinks the Senate version of the NDAA should include language to pre-empt anything the House might try, Fischer did not directly answer, but highlighted that Senate Democrats such as Sen. Martin Heinrich Martin Trevor HeinrichSenate Democrats demand White House fire controversial head of public lands agency Senate Democrats seek removal of controversial public lands head after nomination withdrawal Five takeaways from final Senate Intel Russia report MORE (N.M.), the ranking member of her subcommittee, have expressed support for the triad.

Senate Armed Services Committee Chairman Jim Inhofe James (Jim) Mountain InhofeChamber of Commerce endorses McSally for reelection Overnight Defense: Top admiral says 'no condition' where US should conduct nuclear test 'at this time' | Intelligence chief says Congress will get some in-person election security briefings Top admiral: 'No condition' where US should conduct nuclear test 'at this time' MORE (R-Okla.) has also dedicated many of his questions to witnesses this year to building a case against Smith.

At a hearing with the U.S. general in charge of the nuclear arsenal, Inhofe noted that “some are saying that is an area where we could be making cuts at this time” and asked about the significance of nuclear modernization and keeping all three legs of the triad.

“It is the most important element of our national defense,” U.S. Strategic Command chief Gen. John Hyten replied on modernization. On the triad, he added, “because of the capabilities of each leg of the triad, I have the ability to respond to any threat.”

Asked recently about his line of questioning at hearings and his plans for the defense bill, Inhofe said he hopes to address the “slight disagreement” between him and the House on the issue.

“All of the witnesses have been and said that’s the great single threat that we are facing today,” he said. “I think that we could put to bed the idea that we’re not going to continue with or re-enact our modernization program to put ourselves ahead of our opposition that’s out there being very busy, both Russia and China.”

“I think the main thing is we have the triad,” he added. “That means three, and we got to keep all three defenses out there and in a position that we can use them hoping that it will not be necessary. But if we don’t have them, it would be necessary."