Doubt and skepticism are driving the stock market higher, Jim Cramer told his Mad Money viewers on Monday. 

The S&P 500 finished the first half of 2019 higher by 17%, while the Dow Jones Industrial Average and Nasdaq climbed 14% and 21%, respectively. Those big gains make investors skeptical -- and that's exactly what's needed to take stocks higher. If everyone were bullish and euphoric, the bull market's run would be nearing an end, Jim Cramer said.

That skepticism is exactly what pulled stocks off the highs Monday, after a big opening rally faded in the afternoon. That's despite President Trump agreeing to a trade-war truce with China's President Xi.

The trade war isn't over, but the news should be viewed positively. Just look at what it means for U.S. suppliers to Huawei. They've been banned from supplying components to the company and now suddenly, they'll be able to again.

That's great news for companies like Micron (MU - Get Report) , Skyworks Solutions (SWKS - Get Report) , Broadcom (AVGO - Get Report) , Western Digital (WDC - Get Report) and Qorvo (QRVO - Get Report) , all of which rallied on Monday. Even with the skepticism on Apple (AAPL - Get Report) and Facebook (FB - Get Report) , just look at how these stocks have done this year, up 27.5% and 47%, respectively.

At the end of the day, too many investors and portfolio managers have "one foot out the door" thanks to having doubts about this market, Cramer explained.

When there's good news -- like on Monday -- they're forced to get back in and buy stocks. So while there's a lot doubt out there, remember, it fuels market rallies. Case in point, the S&P 500 hit a new high on Monday, despite the fade.

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First-Half's Biggest Winners

Cramer wanted to take a look at the best-performing stocks in the Dow Jones and S&P 500 from the first half of 2019.

Starting with the Dow, Microsoft (MSFT - Get Report) was the best, rallying 32%. Investors are willing to pay a premium for this mega cap stock, which doesn't have antitrust concerns like Amazon (AMZN - Get Report) , Facebook or Alphabet (GOOG - Get Report) (GOOGL - Get Report) . Cramer said investors can stick with the name.

Visa (V - Get Report) and American Express (AXP - Get Report) are next, up 31% and 29%, respectively. At these prices, American Express is the better buy, he reasoned. Up 27% and Walt Disney Co. (DIS - Get Report) was No. 4 on the list. Long-term investors can stick with this one, but the stock may continue digesting its gains in the near term.

Finally, there's Cisco Systems  (CSCO - Get Report) , which was up 26% in the first half. The company doesn't get nearly enough credit, is still cheap and has a strong balance sheet. Cisco has "more room to run," Cramer said.

Turning to the S&P 500, Cramer nixed Coty (COTY - Get Report)  from the list due to its huge fall on Monday, along with Xerox (XRX - Get Report) , which simply snapped back from a ridiculous fourth-quarter decline.

Chipotle Mexican Grill (CMG - Get Report) surged 69%, while Advanced Micro Devices (AMD - Get Report) jumped 64%. Both are on the move thanks to amazing leadership from their CEOs. AMD is still a buy, Cramer said.

Cadence Design Systems (CDNS - Get Report) surged 62% in the first half of 2019 and could have more upside, as could MSCI Inc. (MSCI - Get Report) , which was up 62%. However, Hess (HES - Get Report) might have run too far, too fast. Investors may want to consider taking profits in this one, Cramer said.

The bottom line? The top five performers from each group are a good group of stocks, and most of them still have room to gain.

Is This IPO the Real Thing?

The IPO market remains hot, with RealReal (REAL) being the latest example. The stock priced above its initial range, then opened higher by 40% on Friday. On Monday, shares slipped 8.1%.

Is it a buying opportunity?

Cramer wants to say yes, but he can't. This well-run online consignment shop is charging forward in a fragmented market of hard-to-find products and counterfeits. RealReal makes it easy for buyers and sellers of luxury consumer items by authenticating the products and selling them online.

RealReal sells all sorts of luxury goods, including apparel, watches, jewelry and even art.

The company has been building a loyal base of users for eight years now and has terrific revenue growth. In the most recent quarter, the company grew sales 49%, while users and orders both jumped 40%. Wow -- what some retailers would give for that growth, Cramer pointed out.

But it's not all good news. The company's margins are heading in the wrong direction and it's not yet profitable. Worse, it's got increasing competition. Even though it's the best run of the group, it can still see its margins squeezed even further. Last, while founder and CEO Julie Wainwright is doing a great job, she was also the CEO of Pets.com, which has become the poster child of the dot-com boom and bust.

At the end of the day, RealReal is a great outfit -- no pun intended -- but the price is just too high. Below $22.50 and Cramer says investors can buy the stock.

Executive Decision: Paychex

On the show's "Executive Decision" segment, Cramer talked with Marty Mucci, president and CEO of Paychex (PAYX - Get Report) . The stock has been bouncing back after last week's punishing post-earnings price action.

Mucci said the company delivered on what most expectations were calling for, and felt good about Paychex moving forward. Revenue grew 12%, adjusted earnings grew 11% and operating margins were solid, he reasoned.

Moving forward, the company is looking for an acceleration in the second half of 2019 and is well-positioned in various end markets. The need for HR support has "never been greater," Mucci said, thanks to all of the new regulations and complexities small- and mid-sized businesses now face. That's a big boon for Paychex.

However, hiring from small businesses will likely slow a bit, he reasoned. Rising minimum wages and a tight labor market make it difficult for these kinds of companies. Admittedly, it's a high-quality problem to have, but it can be difficult to recruit employees to small businesses when the job market has so much demand.

Higher interests were a tailwind for Paychex, but Mucci said investors shouldn't look at that as the company's main catalyst. The fundamentals of the business are driving Paychex, not interest rates.

No Energy for Oil

On the show's "No Huddle Offense" segment, Cramer wanted to talk about oil. Despite crude oil prices rallying, oil stocks remain stuck. What gives?

Even though there's conflict in the Middle East, we simply have too much production capacity in the U.S. Every time oil prices jump, producers sell oil futures and increase production to meet those obligations. Essentially, they are keeping the price of oil from skyrocketing, but continually selling into these rallies.

While higher oil prices benefit oil companies for obvious reasons, the companies can't help securing a profit when they can. In a way, U.S. oil companies are a victim of their own success, Cramer said.

How's this for a comparison: Texas is the world's third-largest oil producer in the world, behind only Saudi Arabia and Russia.

But it doesn't matter. Even on a strong day in the crude market and with OPEC trying to keep oil prices elevated, energy stocks can't maintain any upside momentum. There's simply too much supply, and that makes it tough to own oil stocks, he concluded.

Lightning Round

In the Lightning Round, Cramer was bullish on Advanced Micro Devices (AMD - Get Report) , Yeti (YETI) and Brookfield Asset (BAM - Get Report) .

He was bearish on Xilinx (XLNX - Get Report) , AeroVironmental (AVAV - Get Report) , Intel (INTC - Get Report) , Nio (NIO) and Aramark (ARMK - Get Report) .

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At the time of publication, Cramer's Action Alerts PLUS had a position in AAPL, FB, MSFT, AMZN, GOOGL, DIS, CSCO.