The political momentum in the gun control debate has shifted in the year leading up to this weekend’s mass shootings in El Paso and Dayton, Ohio, with gun control advocates taking a more empowered stance and the National Rifle Association consumed by internal power struggles.

The major gun control organizations, propelled by funding from supporters like Michael R. Bloomberg, the former New York City mayor, and grass-roots networks across the country, have helped enact new laws — mostly in Democratic-controlled states — and, for the first time in 25 years, passed a significant gun control bill in the House.

But the gun lobby’s structural advantages, built over decades and defended by President Trump and congressional Republicans, remain in place: an N.R.A. budget that dwarfs what even Mr. Bloomberg has spent, a Republican Senate majority disinclined to consider gun-control legislation, and a base of primary voters for whom the N.R.A.’s endorsement is a critical seal of approval.

The net effect is a playing field on gun issues that is far more level than it has been since N.R.A.-backed Republicans took over Congress in 1994, sparking one of the country’s most bitter, partisan culture wars.  […]