Stocks decided to take a breather at the end of May, bringing up many questions ahead of summer about just how strong and powerful this bull market can remain after six years. The bad news is that each rally feels like it reaches exhaustion quickly. The good news is that investors have lined up in droves for almost four years now to buy their favorite stocks on every pullback.

24/7 Wall St. has looked closely at which stocks leading the market and which are hurting it. With a 2015 projection of 19,142 for the Dow Jones Industrial Average (DJIA), our initial estimate was that the Dow might gain 7% or so in 2015, with a handy portion of that coming from dividends.

It turns out that six of the 30 Dow stocks are hurting the broader index so far in 2015. Now that May has come to an end, 12 of the 30 Dow stocks are running in the red with negative performance, if you include their dividend payments. The other 18 Dow stocks were positive. The median loss of the 12 losers was 6%, while the median gain among the 18 winners was right at 7%.

According to IndexArb.com, each of the six Dow stocks hurting the market also have average index weightings since the Dow is a price-weighted index rather than a market cap-weighted one. 24/7 Wall ran the year-to-date performance of each of the six worst DJIA losers, and we included the loss and the weighting in the Dow (from IndexArb).

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The losers in order of worst performance (worst to least-bad) were as follows:

• American Express Co. (NYSE: AXP)
• Procter & Gamble Co. (NYSE: PG)
• Wal-Mart Stores Inc. (NYSE: WMT)
• Exxon Mobil Corp. (NYSE: XOM)
• Chevron Corp. (NYSE: CVX)
• Caterpillar Inc. (NYSE: CAT)

When 24/7 Wall St. gave its indication of a 19,142 peak in the Dow in 2015, we also ran a bull and bear analysis for each of these Dow giants. Some have done exactly as expected, but some have offered surprises as well.