Top White Houseclimate aides have shared a little more of their thinking about its massive climate spending proposal.

Why it matters: The White House is facing intense political pushback on the plan's size, so their success or failure at justifying its costs could matter in Congress and the ballot box.

They're emphasizing the cost of inaction. While the package has a hefty price tag, so too does inaction, both in damage from extreme weather events and geopolitics, the aides said.

• "Every year that we delay, we're talking about other countries racing ahead to seize that competitive advantage in these incredibly important industries of the future. So, the cost of inaction is mounting already," said Gina McCarthy, President Biden's top domestic climate adviser.

The plan's link to a looming deadline is tricky. The Biden team has an April 22 deadline to unveil a closely watched 2030 emissions target — and convince the world it's credible.

• The spending plan's legislative fate will still be unknown, so officials need to figure out how to finesse those timelines.
• McCarthy said Thursday that the emissions target under the Paris deal (called a "nationally determined contribution") will rest in part on the big investments they're asking Congress to approve.
• But she also emphasized executive steps, citing the new multiagency initiative to expand offshore wind power development. And more broadly, officials are planning new emissions regulations under their existing powers.

The sales team is in place. Biden yesterday named five Cabinet heads who will take the lead in pitching the plan to the public and Congress:

• Transportation Secretary Pete Buttigieg, DOE's Jennifer Granholm, HUD's Marcia Fudge, Labor's Marty Walsh and Commerce's Gina Raimondo.

They're really not into carbon pricing. McCarthy offered a careful but pretty clear signal that carbon taxes or cap-and-trade isn't part of their thinking.

• She told reporters that while Biden's open to ideas, their Capitol Hill focus is on big investments and the proposed "clean electricity standard."
• "This reflects his interest in making sure that he meets his commitment, and that he uses the best tools available and that's what you see in front of you," McCarthy said.

Sizing up the White House spending goal: Nonprofit World Resources Institute's analysis — which is supportive of the proposal — says at least $1 trillion would "go to sectors that fall under the broad umbrella of climate change, clean energy and environmental justice."

Of note: Those tallies don't include the cost of the Biden plan's new and expanded tax credits around renewables, electric vehicle purchases, transmission and more.

• The research firm Capital Alpha, in a note, estimates those costs at around $300 billion over 10 years.

What to watch: Republicans' criticism of Biden's infrastructure package isn't just about its cost, but also the definition of "infrastructure."

• This time around, they'll try to convince voters the infrastructure legislation is more of a wishlist for progressives than a "roads-and-bridges" measure, Axios' Lachlan Markay and Alayna Treene report.