The Dow Jones Industrial Average (DJINDICES:^DJI) has dipped into mildly negative territory in afternoon trading, down 0.05% just before 2 p.m. EDT. Intel (NASDAQ:INTC) trails the blue-chip index at a greater distance than any other Dow member, losing 1.3% of its value.

What's wrong with Intel today?

The damage comes from Nomura Securities analyst Romit Shah, who published a very conservative research note on Intel.

The firm has a neutral rating on Intel shares, which it reiterated while lowering the share price target from $27 to $25. Above all else, Shah said that Microsoft's (NASDAQ:MSFT) newly released Office apps for the Apple (NASDAQ:AAPL) iPad tablet are a big minus for Intel.

"We are surprised that Intel shares shrugged off news that Office would be available for the iPad," Shah wrote. "The enterprise notebook market is considered very defensible for Intel. However, the availability of Office on the iPad is significant in that it's the first time Microsoft's productivity suite will run on non-Windows, non-x86 based devices."

Which of these Apple devices will rule the office market tomorrow? Consider the answer to that qyestion very carefully, because Intel's future may hang in the balance.

In other words, Microsoft is letting Apple steal some of Intel's traditional thunder. Intel chips have so far been nearly mandatory for running serious business applications like Microsoft's crucial Office suite. But iPads don't have Intel inside, being built around ARM Holdings (NASDAQ:ARMH) chip architectures. Apple designs these chips to its own specifications and farms out the manufacturing of the final product -- and Intel never touches this supply chain.

Shah's theory is more than just high-level speculation, too. "Overall, the enterprise notebooks have been stable at 20m units per quarter over the last three years. But we see a changing mix in corporate adding incremental pressure to Intel's PC Client business over the coming periods," he wrote.

In other words, the Nomura analyst sees tangible evidence that Intel's corporate PC market is taking a hit from Apple's tablets.

Now, Intel is trying hard to establish itself as an alternative for tablet and smartphone builders, on par with ARM. But these efforts have not gained much traction so far, and it's very difficult to find Intel-based tablets on store shelves to this day.

So it makes sense for recently appointed Microsoft CEO Satya Nadella to stretch Redmond's most important product line onto the Apple ecosystem. Even if the company might hurt longtime partner Intel in the process.

The takeaway for Intel investors
Shah's argument makes sense. It's easy to see how Microsoft's Apple-friendly move could bring a wind of change into the corporate computing world.

Some jobs will always need a full-blown PC system (or Mac, though those are currently based on Intel chips as well), but iPads and other tablets can make a handy replacement for laptops in many situations.

As an Intel shareholder, I'm starting to get nervous for several reasons:

  • The mobile push isn't working out as planned.

  • Former friends like Microsoft are becoming frenemies -- at best.

  • Intel's once super-dependable dividend boosts have disappeared, leaving the payout stuck at $0.225 per share since summer 2012.

Intel has been a money maker in my portfolio, but I would have done just as well with a simple Dow tracker in its place.

INTC Chart

INTC data by YCharts.

Today's analyst note is not an indisputable "sell" signal for Intel investors, but the body of negative evidence is starting to pile up. Maybe it's time to take a closer look at that old investment thesis on Intel, just to make sure it still holds water.

Right now, I'm not 100% sure that it does.