Craig Moffett, senior analyst and a partner at MoffettNathanson Research, who has been closely following these developments, pointed out that Sept. 4 was when Tom Wheeler, the F.C.C. chairman, said in a speech that “there is simply no competitive choice for most Americans” who want high-speed Internet in their homes.

Image Tom Wheeler, chairman of the Federal Communications Commission. In September, he said in a speech that “there is simply no competitive choice for most Americans” in home high-speed Internet service. Credit... Daniel Rosenbaum for The New York Times

“Stop and let that sink in,” Mr. Wheeler said. He added that “three-quarters of American homes have no competitive choice for the essential infrastructure for 21st-century economics and democracy.”

Mr. Moffett said of those words: “That was a very strong speech for the chairman of the F.C.C. The market took notice.”

One core problem for Comcast and Time Warner Cable is that after a merger, the combined company would control more than 35 percent of the market for high-speed wired Internet service, even after divesting itself of some customers. If, as Mr. Wheeler said, that market is not competitive now, a merger of the two biggest cable companies would not help matters.

In October, the price spread widened further, to well above 10 percent at several points. In the last week or two, it has oscillated between 8 and 10.5 percent. Again, market action came after news that might have caused investors to do some recalculating of the future profitability of Comcast and Time Warner Cable, either as independent companies or as a merged entity.

One market flurry occurred after remarks by President Obama at an Oct. 9 town hall meeting in Santa Monica, Calif., in which he said he was “unequivocally committed” to net neutrality and against “paid prioritization,” or Internet fast lanes, in which some companies could pay cable companies for faster access to consumers. He called for tough rule-making by the F.C.C. — which could potentially limit the profitability of the cable companies.

And late last month, people close to the F.C.C. said the commission was considering several options for net neutrality rule-making. These include regulating Internet infrastructure companies more strictly — as common carriers, like the old telephone companies — under Title II of the Communications Act of 1934. Such regulation would be imposed over wholesale interconnections between information providers and broadband carriers like the cable companies. Under one possible plan, less stringent regulations would be imposed by the agency for Internet connections from cable companies to customers.