WASHINGTON — An explosion of spending on political advertising on television — set to break $2 billion in congressional races, with overall spots up nearly 70 percent since the 2010 midterm election — is accelerating the rise of moneyed interests and wresting control from the candidates’ own efforts to reach voters.

In the first full midterm cycle where outside groups have developed a sophisticated infrastructure, the consequences are already becoming apparent: a harshly negative tone dictated by the groups and a nearly nonstop campaign season that could cause voters to tune out before Election Day.

“They have become a shadow party that’s effectively impossible to dislodge, and they will shape, if not control, the dialogue in key races and therefore nationally,” said Sheila Krumholz, the executive director for the Center for Responsive Politics. “All of this sets the stage for 2016.”

The phenomenon, which is playing out in races across the country, is particularly pronounced in several competitive Senate contests — in places like Alaska, Colorado and North Carolina, among others. In the Senate races alone, the number of political television spots from outside groups is nearly six times as much as it was at the same point in the 2010 cycle. In fact, more political ads from outside groups have already aired during the relatively slow summer period of the 2014 Senate contests — roughly 150,000 spots through mid-July — than ran throughout the entire 2010 Senate elections.