The $484 billion relief measure that President Trump signed on Friday is a vivid example. The impetus was an emergency: The small-business loan program created by the stimulus law ran out of money days after it was enacted, as distressed companies sought forgivable loans to help keep their operations humming. So Congress swooped in with $320 billion to refill its coffers. That would not have been necessary had lawmakers heeded original calls to devote far more money to small-business relief in the initial $2.2 trillion stimulus law.

The measure also contained $75 billion for hospitals and $25 billion for testing — but neither sum comes close to what experts project will be needed, which many of its proponents conceded.

Congressional leaders have not funded the significant scale-up in testing and tracing of Americans that experts say is necessary to give consumers and workers confidence to return to something resembling normal life while the virus still poses a deadly threat. Nor have they settled on a strategy to keep aid flowing should the virus continue to suppress economic activity through the summer and beyond. Those decisions could have damaging consequences — by not spending more on testing today, lawmakers could find themselves under pressure to continue support for people and businesses indefinitely.

Now, Republicans and Democrats are clashing over the scope and timing of the next aid package — particularly whether it should contain relief for state and local governments whose budget pictures are dire — with no action expected until May. Republican lawmakers signaled they were returning to concerns about how much Congress was adding to the national debt with all of its government spending.

“It’s time to begin to consult with experts — people who make a living doing this kind of thing — and weigh the impact of all of this,” Senator Mitch McConnell of Kentucky, the majority leader, said in an interview. “Knowing full well this is necessary, nevertheless, that doesn’t mean you close your eyes to the impact you may be having on the country’s financial viability in the coming years.”