Oh, I see. Their lead sentence threw me off. I thought they were talking about all of Europe.
The countries concerned are all paid-up members I suppose.
These countries (excepting Sweden) are what Rumsfeld called "New Europe", as opposed to France, Britain and Germany, that dominate EU. The liberated themselves from the USSR and, naturally, joined whatever Western organizations would take them. They all are now having second thoughts about the EU, but they are enthusiastic members of NATO . The did not engineer the refugee crisis in Europe: Merkel, the German Chancellor did. They tend to be conservative and pro-US, at least in foreign policy.
Bulgaria is on the receiving end of the refugee flow from Turkey. The refugees are not staying in Bulgaria, they pass through, because they want to go to the rich countries of Europe, primarily Germany. The rest of the countries on the list do not accept refugees. See the map: Map of Europe refugee crisis.
Trump, or any American president, will have to deal with two geopolitical crises, not one. It is, indeed, the Muslim invasion, now in the form of refugees, but also the migration from Islamic countries to the former colonial powers such as Britain and France. That is made worse by the European Left. But that is not a problem that Poland and the Balt republics contribute to. Bulgaria and Hungary (whose politicians are also on the list) would like to stop the flow, but they are geographically on the refugees' way and the EU dictates open-borders policy. Neither of these countries is the target of migration, West Europe is.
The second crisis we will have to deal with is the resurgence of Russian aggression. That is what the article is about. No, it does not mean we need to go and die for Crimea right away. It means that we do not appease aggression, because otherwise after Crimea and Ukraine Putin will turn to the Balt republics and Poland, and they are NATO members.
Judging by the Mattis and Tillerson testimonies recently, the incoming administration understands that Putin and Russian belligerence will be a problem.