TBH, this might be true. Remember that I used the word "might" because he's just speculating.The economic situation in the United States has worsened not because Biden became president. Now all countries are experiencing a decline in their economy and the reason for this is the consequences of the long-term fight against coronavirus, which led to a drop in production and inflation, wars, sudden climate change, natural disasters and much more.
I'm not from the US, but I saw how both Trump, and Biden became a president, and I would say that the country is better with Trump as their president. What's happening with the country now that their president is Biden? The buying power of their currency went down, and average people barely survived with their day-to-day job. An average person can't afford to buy their own home because the prices of houses right now are just too high compared to their daily salary. I mean it's just worse compared to when Trump is their president.
His warning is more of a blackmailing for me for him to win and he can't back that statement with data and proof, but I like him to win this upcoming election though.