It's simple, really...

The Border The TreatyWhy?

In the new Northern U.S. In the new Southern U.S.
Abortion Would remain available, safe, and legal. Would likely be made illegal. Women who have abortions and a doctor who performed an abortion would be imprisoned or executed.
Health Care Socialized health care, free for everyone, including mental health, vision and dental care. No health insurance companies or health insurance systems. Privatized health care, as unregulated as possible (pre-Obamacare, so pre-existing conditions exclusions would return.) Insurance companies would remain the best option for coverage.
Taxes Higher taxes than the South. Lower taxes than the North.
Commerce New regulations to protect consumers and curb risky investment practices at large financial institutions. Increased deregulation of financial institutions.
Jobs Government investment in job stimulus, including re-education and unemployment benefits. Decreased taxes on corporations, reduction in length and amount of unemployment compensation.
Gay Rights Gay marriage and domestic partnerships would be legalized in all states and at the federal level, with no discrimination between straight and gay relationships. Gay marriage would likely be made permanently illegal via constitutional amendment; only straight marriages would be allowed. Unlikely that domestic partnerships would be made legal. Protections for gays in hiring, housing, etc. would likely be overturned.
Separation of
Church and State
Courts would enforce a sectarian society where region is free to practice but public property and spaces would be neutral. Religious organizations might be taxed. Prayer in schools and religious sponsorship of public events and spaces would likely become legal. Elements of Christianity would likely be infused into new laws. Churches would become more powerful and be more able to influence politics and remain tax-exempt.
Social Security The retirement savings program would likely be enlarged with eligibility age reduced and benefit amounts increased. Social Security would likely be eliminated completely. New savings plans might be designed, but offered by corporations, not government.
Medicare Would be eliminated as unnecessary, since Health Care would be socialized (see above). Medicare would likely be eliminated completely. Seniors would be expected to purchase health insurance on the open market. New groups for elders might be offered by insurance companies.
Medicaid Would be eliminated as unnecessary, since Health Care would be socialized (see above). Medicaid would likely be eliminated completely. People would purchase health insurance on the open market.
Drug War The "War on Drugs" would likely be eliminated and pot would be made legal. Other drugs might be made legal over time. The "War on Drugs" would likely be continued, with all drugs currently classified as illegal remaining so.
Armed Services All branches of the military would be paid higher wages and after service, veteran benefits would likely be increased. Outsourcing would likely be curtailed. Wages of service-members would likely remain at current levels, and more outsourcing of military activity would occur. Increased spending with military vendors.
Welfare Likely to remain as currently designed. Would likely be eliminated completely.
Infrastructure New technology such as high speed rail and alternative energy systems would be developed and instituted. More repair of existing infrastructure. Neither high speed rail or alternative energy would likely be funded. More roads would be built.
Death Penalty Likely abolished. Likely mandated.
Foreign Policy More UN involvement, more humanitarian missions, less occupation missions. More conflict/occupation missions, less humanitarian missions.
Immigration A naturalization path for existing illegal immigrants and a controlled border policy for new immigrants. A deportation policy for existing illegal immigrants and a controlled border policy for new immigrants. Likely a physical border constructed/enhanced along Southern US/Mexico border.
Civil Rights Enforcement of existing civil rights laws would increase and new laws designed to bolster equal opportunity would be passed. Unknown if existing civil rights laws would be curtailed or eliminated, but enforcement would likely be de-funded and new laws for equal opportunity would be unlikely. Affirmative Action would likely be eliminated.
Education Increased federal support of local education, including Headstart and college, and college loans. Decreased funding for all education likely; possible elimination of the Dept. of Education.

So, which country would you rather live in? If we divide, it could happen!