WASHINGTON — Defense Secretary Jim Mattis said a $30-billion boost in defense funding this fiscal year will produce immediate readiness dividends for the military, but Senate Democrats shrugged off his promises as an unrealistic, incomplete plan.

Lawmakers have until the end of next month to pass a budget for the final five months of fiscal 2017, after operating for months under a continuing resolution at last year's funding levels.

President Trump has asked for a sizable jump in military funding right away, part of a multi-phase plan to boost defense spending and "rebuild the military" to address terrorist and hostile state threats against America today.

Mattis, in his first appearance before Congress as a Cabinet secretary, told members of the Senate Appropriations Committee that 15 years of war and the resulting deferred maintenance and training have left his department in need of immediate help, justifying what he acknowledged is a difficult funding request.

"This increase in funding will help address the worsening security situation confronting us around the globe," he said. "We must recognize that hesitation now to invest in defense would deepen the strategic mismatch between our future security and the military means to protect our people and freedoms."

He said with the extra money, the Pentagon could double the number of deployment-ready Army brigades this year, as well as "get our aircraft back in the air, our ships back to sea." Mattis pushed back on Republican criticism that the $30-billion boost is too low, calling it "the number we believe we can execute responsibly" given the half-finished fiscal year.

But despite Republican support in the House and Senate for the plan, passage of the budget boost remains problematic given Democratic opposition.

Among their objections on Wednesday to the budget plan Trump sent to Congress: It violates automatic spending caps put in place in 2011, it cuts billions from non-defense spending to pay for the increased military money, and it asks for $5 billion in new funding to combat Islamic State group terrorists without a promised accompanying new strategy for that fight.

Senate Appropriations Defense Subcommittee Ranking Member Sen. Dick Durbin, D-Ill., called the plan an "extremely reckless plan" and "an incomplete budget that does not address problems in a serious way."

He said if the plan were to pass as presented, it would trigger an automatic 5 percent across-the-board budget cut to Defense Department accounts because administration officials opted not to include a formal sequestration repeal in the plan.

"I don’t know why they’re playing games," he said.

Sen. Patrick Leahy, D-Vt., stated that "slashing non-defense spending to pay for defense is not a solution." Democrats for the last six years have blocked Republican plans to increase military spending without more fiscal freedom for other domestic priorities.

Mattis offered little protest to those criticisms, even agreeing with Durbin’s description of the budget proposal as incomplete.

But he said the defense funding situation — "my responsibility" — needs immediate resolution, noting that "looming threats have outstripped the level of resources we have been allocating to defense."

House lawmakers have already passed a fiscal 2017 defense appropriations measure, and Senate Appropriations Defense Subcommittee Chairman Thad Cochran, R-Miss., said he hopes to move on the issue soon.

But Democrats have said they won’t move ahead with the defense budget until other domestic spending plans are also outlined. And Senate Democratic leaders have threatened to block any fiscal 2017 funding plan if it includes money for a southern border wall, one of Trump’s top spending priorities.

Leo Shane III covers Congress, Veterans Affairs and the White House for Military Times. He can be reached at lshane@militarytimes.com.