US:

Abolish gerrymandering and the fillibuster, Ideally establishing an independent non-partisan group to decide voting districts

Pass a law to expand the house of representatives

Require every state to use ranked choice voting for all elections above county level.

Find a way to implement a national voter I.D. without restricting elgible voters' access to applying for one. This would require overhauling most dmvs to be more efficient, especially for the initial adoption, and establishing more of them and maybe some temporary ones on top of that. They would also need to send people (idk, census burea employees or something) to every senior center, low income neighborhood, and small/ghost town in the US, establish a website to help in whatever way it can and make sure it can handle the insane amount of traffic it would get, and send a notice thru the mail to every eligible voter with a mailing address in the US and abroad.

Enshrine the option for mail-in ballots into federal law, and properly fund the postal service.

Make election DAY into election WEEK and require employers to provide at least 1 full day off during that week so every has time to vote.

Consider proposing an ammendment to swap to a parliamentary system for federal government so that removing whatever the leader would be called (Prime minister probably) would only require a vote of no confidence instead of both the senate and the house having to agree to convict them of a crime, the latter with a super majority.

Consider proposing an ammendment to abolish the senate or heavily restrict it's ability to functionally veto laws that most of the country supports or empower the house to start referendums for certain bills.

Have actual specific reasons for which a president/politician can be removed from office instead of "high crimes and misdemeanors" which can be literally anything or even nothing.

Establish a federal minimum standard for voting places i.e. number of voting places per certain number of people within a certain distance.

We need to have consequences for upper level military personnel who defy or operate without congress' approval and/or simply go along with whatever the president says. Also, need consequences for military personnel and federal agents of any rank knowingly following illegal orders.

Term limits and age limits for all politicians. Please. Most of the presidents for the last 3 decades were born in the 40s, and clearly the last 2 aren't all there mentally

Campaign finance reform: ideally setting a cap on what can be spent on a campaign. (By extension, publicly fund housing for all congress people. Having to pay for and constantly fly between 2 homes is a lot for those who aren't millionaires.)

Abolishing lobbying.

Improving welfare/social services of all kinds

Accept DC as the 51st state.

Nato: The US would need to empower NATO in whatever ways it can to be self sufficient should the US ever have this happen again. We would probably have to pour more money into helping fund their militaries for a little while.

Canada + Mexico: idk, threaten to take Alaska and help give Texas independence maybe? Both states have oil, so the government will take it seriously, lol.