On Tuesday, the U.S. markets reached a milestone. The S&P 500 is on track to enter its longest-ever bull market, which began 3453 days ago on Mar. 9, 2009, when the index was at 666. It has since more than quadrupled, reaching a new 52-week high intraday of 2,873.
CNBC's Jim Cramer named the top 10 obstacles the market had to overcome in order to achieve this record. But with news of President Donald Trump's former lawyer pleading guilty to violating campaign finance law, "investors got a whole new reason to sell," said Cramer. "I can't tell you what will happen with this new set of worries."
Here are Cramer's top 10 worries that the bull market has overcome in the past:
1. Skepticism
According to Cramer, the bull market skeptics actually helped to fuel the rally. "Crucially, this skepticism is the main reason for the bull's longevity," the "Mad Money" host said. "This run would have ended if investors had ever gotten too euphoric."
2. High valuations
Many investors have argued that stock prices are too high given companies' earnings numbers. However, thanks to tax reform measures companies have been able to beat Wall Street's earnings estimates and deliver consistent growth, pushing the market higher.
3. Political turmoil
From congressional gridlock to the 2016 presidential elections to the looming trade war, "the bulls had free reign" throughout all kinds of political conflicts.
4. The Fed
The Federal Reserve has consistently raised interest rates since the end of 2015. Higher rates means higher returns for bonds, making them more competitive with stocks. Cramer thinks that this hasn't come to pass because even with consistent hikes, rates are still relatively low at 2 percent.
5. U.S. debt downgrade
According to Cramer, one of the darkest moments in the bull market was when S&P downgraded U.S. government debt from AAA to AA+ in 2011.
6. Industry bear markets
Although the overall market has rallied, hidden within the broader trend are "smaller bear markets that are mauling entire sectors," Cramer said. He pointed to the housing industry, oil and semiconductor industries as examples.
7. European woes
The economic troubles of various European nations, such as Greece, Italy and Turkey, have tested the global markets. In every case, Cramer has believed that "these exogenous issues will be solved."
8. China worries
Prompted by fears of an economic slowdown in China, the flash crash of 2015 "caused tremendous pain the U.S." Cramer said. "But these days we're in fear of anything China does."
9. Inverted yield curve
Conventional wisdom says that when the 2-year Treasury yield rises above the 10-year Treasury yield, a recession is on the way. We're nearing that point now, but Cramer is "not concerned about it because we have been living with this threat for ages, and it hasn't proven to be a problem."
10. FAANG fallout
The group of tech stocks - Facebook, Amazon, Apple, Netflix and Google - have continued to gain market cap over the years while also being "scorned by most professionals as being overvalued," Cramer said. He believes that the group will continue to thrive due to its constant innovation.
Cramer's bottom line
"You want to know why this bull market has lasted so long? It's because the bull was an underdog the whole way. The whole time it felt like the bears were right at our heels. And that's what gives us the fuel to keep going higher."
Disclosure: Cramer's charitable trust owns shares of Amazon, Apple, Alphabet and Facebook.
WATCH: Cramer lists the bull market's top 10 obstacles
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