Assassin by gun is objectively more difficult in a country that bans them outright. His ardent support for private gun ownership contributed to the continuation of a nation filled with more guns than humans.

I do think the United States needs to overhaul its firearms laws, however:

There are very few countries that ban firearms outright. The type of weapon used in this attack was a bolt-action hunting rifle. You can buy that sort of weapon on the basic firearm license in Canada, the UK, Australia, Germany, Norway, Sweden, etc.

The entire gun debate in this country which usually revolves around tightening restrictions on handguns and semi-automatics is not really relevant to this case. Virtually nobody running for public office, even among Democrats, is talking about a total ban on private firearms ownership.