In an interview, Democratic Senator Sheldon Whitehouse of Rhode Island blamed the sweeping rollback of environmental protections on a flood of unlimited, anonymous corporate political spending, and said exposing the scale of this "fraud" is key to breaking its grip.

His remarks came as the death toll from catastrophic flooding in Texas linked by scientists to climate change threatened to surge further.

"This isn't even government any longer," the 69-year-old told a small group of reporters ahead of an address to Congress Wednesday -- his 300th so-called "Time to Wake Up" speech, delivered as activists reel from Trump's actions.

"This is an occupying force from the fossil fuel industry that has injected itself into the key positions of responsibility," said the lawmaker.

"It has the appearance of being government -- they ride around in the black cars... they have the offices, they have the titles," he said. But in reality, "they're fossil fuel flunkies... and they care not a whit for public opinion or public safety."

Big Oil spent at least $445 million to help elect Trump, according to a recent analysis by Climate Power, which said its figure was likely a vast underestimate because of undisclosed donations.

- Dark money takeover -

In his second term, Republican Trump has pulled the United States out of the Paris climate accord, gutted science agencies, fired researchers and forecasters, scrapped his predecessor Joe Biden's clean energy tax cuts and rolled back powerplant and vehicle efficiency standards.

Whitehouse calls it the oil, coal and gas industry's "most sordid dreams come true" and says the stage was set by the 2010 Supreme Court "Citizens United" ruling, which unleashed an era of unchecked corporate political spending.

A former state attorney general who battled corporate polluters, he recalled that when he first joined the Senate, climate bipartisanship flourished: John McCain, the GOP's 2008 presidential nominee, had "a perfectly respectable climate platform," while Republican senators proposed bills.

"These weren't little tiddlywinks, nibble-at-the-edges bills," he recalled, but would have genuinely changed the trajectory of climate emissions.

Citizens United reversed century-old campaign finance restrictions and opened the floodgates to dark money.

"They were able to come into the Republican Party and say, 'We will give you unlimited amounts of money. You will have more money in your elections than you've ever seen before.'"

- The way forward -

Despite the bleak landscape, Whitehouse still sees a narrow path to climate safety - and points to several potential game changers.

First, he cites the possible emergence of a global carbon pricing effort, spearheaded by the European Union's Carbon Border Adjustment Mechanism, which taxes importers based on their climate footprint.

Countries like the UK, Canada, Mexico and Australia could join this movement, creating a de facto global price on carbon, enforced through trade -- without US legislation.

Second, he says, Democrats can and must expose fossil fuel's stranglehold on the Republican party, a phenomenon he calls one of the "most grave incidents of political corruption and fraud that the country has ever seen," and pass a bill forcing donor transparency.

Third, what was once framed as a crisis for polar bears -- and later as an opportunity for green jobs -- is today directly hitting Americans where it hurts most: their wallets.

Federal Reserve Chair Jerome Powell has warned that climate change will shrink mortgage availability across swaths of the United States in the coming years as banks and insurers retreat from fire- and flood-prone regions.

Risks could cascade from an insurance crunch into a broader mortgage collapse -- potentially triggering a 2008-style crash.

Whitehouse predicts the fossil fuel industry's hold on Republicans won't last forever.

"When it becomes clear what has been done here, then there's going to be a dramatic reset," he said. "A reckoning will come for this. There's no doubt about it -- it's just the nature of human affairs."

Trump himself, he added, was merely swept along by the dominant current of the post-2010 Republican Party, with no ideological stake in the issue. As recently as 2009, he co-signed a full-page advertisement in the New York Times demanding stronger climate action from then president Barack Obama.