Look to the stock market and youd assume Wall Street was doing just fine. The S&P 500 has come back to March highs, the Dow is back to positive for 2018, and the Nasdaq is at fresh records.

Its all built on shaky foundations, said longtime market bear and former Republican Congressman Ron Paul.

This market is in the biggest bubble in the history of mankind, and when it bursts, it could cut the stock market in half, he told CNBCs Futures Now Thursday.

I see trouble ahead, and it originates with too much debt, too much spending, Paul said.

This isnt the first time Paul has made such dire warnings. During a Futures Now appearance in August 2017, he predicted a 50 percent drop in the market, a call he has doubled down on a number of times since. Since that appearance, the S&P 500 has rallied 15 percent.

Paul belongs to the Libertarian Party, a faction that emphasizes constrained government spending. He sees federal spending and monetary policy as dual forces inflating a market bubble.

The Congress spending and the Federal Reserve manipulation of monetary policy and interest rates debt is too big, the current account is in bad shape, foreign debt is bad and its not going to change, he said.

Paul isnt alone in his critique. A number of politicians have voiced concern over ballooning deficits, including current House Speaker Paul Ryan, who raised a warning on the nations debt in 2012.

The Congressional Budget Office estimates that federal deficits will average $1.2 trillion a year from 2019 to 2028, according to its April economic outlook. Its 2018 deficit estimates rose by $242 billion over previous forecasts made in June 2017. The federal agency said the revision was mainly owing to lower projected revenues tied to tax reform.

We have a president who likes to spend. He is not concerned about the deficit, said Paul.

To Paul the decision-making arm of the Fed is equally at fault in creating a market bubble.

The Fed will keep inflating, and that distorts things, Paul continued. Now theyre trying to unwind their balance sheet. I dont think theyre going to get real far on that.

The Fed is more than two years into its rate-hiking cycle. In conjunction with rate hikes, the Fed is also unloading assets from its balance sheet, which expanded to $4.5 trillion during its post-financial crisis quantitative-easing program.

Paul is not confident much will change to divert from the disaster he predicts.

The government will keep spending, and the Fed will keep inflating, and that distorts things, said Paul. When you get into a situation like this, the debt has to be eliminated. You have to liquidate the debt and the malinvestment.

Paul reiterated his call on Thursday for a potential 50 percent sell-off on the stock market.

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Ron Paul warns that this is the 'biggest bubble in the ...