Well, I've solved the whole problem of these obdurate United States by simply building on what is already in existence or soon will be. Some of it is the result of this whole idea of the "nation" being coast-to-coast but empty in the middle. We know that the West Coast will fall into the Pacific any day now. The East Coast will soon be submerged by the rising sea level of the Atlantic, so that solves the problem of all that aging architecture and population that thinks it's so important and soaks up so much energy. It will also wipe out the ports for those aberrations of the middle class called cruise ships.
These changes are probably decades out, about the time the actual temperature and habitats across the country are transformed. It's hard to envision because it's not just a matter of getting hotter and hotter. As we already are experiencing, global climate change means hurricanes and so on are becoming much more intense and coming much more often. Cancel out the unfair and unreasonable government flood insurance program and the now-obsolete flood plain maps, and rule that if anyone's house gets flooded, they will be responsible for tearing it down, clearing the land, removing the debris and moving somewhere else.
Once the Panama Isthmus is underwater so both the country and the canal are gone, the currents that push water in huge currents around the seas will seek new paths, totally changing the way they carry heat in global cycles and cause top-to-bottom turnover so that the Japanese current will no longer warm the West Coast and the temperature of Britain will be so cold that everyone will "Brexit." This will also change shipping and ocean life -- fishes and the like who depend on the cold water brought to the surface.
Likewise, whopping changes like land rising once heavy ice is gone, carbon released by formerly frozen land, and plate tectonic movement that produces massive earthquakes, volcanoes, and changes in underground water, will transform the atmosphere in ways we never expected. To go outside, we may need to wear a hat and a gas mask.
Nevertheless, as in the Northwest, cities will dominate demographics and provide services, including agreeing to maintain the infrastructures that unite us, like the highway system and airports. Ways to insulate the internet and other computer functions will probably start in this NW locale since there are so many techies, but much will be redesigned for people to use in family or neighborhood units, capturing local energy sources like wind, sun, and whatever energy storage units can be devised. Transformers and high tension lines will be obsolete.
The problem of the "wall" between Texas and Mexico is easily solved by giving Texas back to Mexico -- maybe along with New Mexico -- and forbidding international corporations from moving back and forth, which won't cost much since it's a matter of paper and maps. The wall that was supposed to be along that border will be built instead around Washington, D.C., actually a dam to keep the ocean out of all the fine memorials we love.
The White House and the attendant Congress with its supporting functions will be moved to the middle of the continent, but not far enough to interfere with the Mississippi flood plain which will no longer be managed by engineering (dams and levees), since that approach isn't working even now. No lobbying businesses will be allowed to locate within a hundred miles of this new capital; however, arts and humanities groups will be subsidized.
Existing states will be asked to form coalitions on the way to redrawing and renaming themselves according to eco considerations. State efforts at gerrymandering will be discouraged. Considerations of population numbers must include the possibility of decimating new diseases and insect plagues, and take into consideration declining fertility and shorter mortality as we are seeing now. Nepotism will be banned. No millionaires, billionaires, or lawyers will be allowed to hold elective office or be on the president's cabinet.
Since materialism and commerce are now the basic justifications of government, serious thought in each state will be given to what can be built, mined, formed, and what rules should govern these acts. But an effort will be made to design effective and humane rules for sustaining life of all kinds, including humans, and providing basic needs like shelter, food, clothing, green spaces (if possible in those ecosystems), and the like. In doing this work, committees must always include at least one person with close links to indigenous people's past. Traditional methods of wealth re-distribution must be observed. For instance, the potlatch in the Northwest which was a feast and giveaway, or the gifting ceremonies that Plains people use today to celebrate ancestors.
Education will be provided for all at no cost, but will be redesigned to mesh with child-rearing practises that will produce people who have the skills needed for that area and will motivate them to maintain the loop that encircles formal classes, public service, 100% citizen participation, partnerships across generations, and constant communication with the rest of the planet.
I don't know what to say about sex except that it will always be there in spite of infertility and find its own way, but criminalization, stigma and victimizing the younger and weaker are not the way. Variation should be welcomed. Binary gender-based enterprises that count on and enforce compliance must find new ways that are not so formed by compliance with the past. Fashion is there; sports is not.
Violence, force, incarceration and guns are beyond my ability to grasp, but careful attention must be given to how they intermesh with medical care, particularly preventative measures based on bad science and a medical/military model for handling mental issues.
This whole line of change will be opposed, undermined, and treated with various kind of terrorism. Once achieved it will be hard to maintain. Do it or lose the species.