After Trump tweets, how is immigration really affecting Europe?

"It's been one of the biggest crises that the European Union has faced in a decade where there have been several crises in a row," John Springford, deputy Director of the Centre for European Reform, tells CBS News. The European Union is a borderless travel zone, meaning that once someone enters, he or she is able to move between EU countries freely. This "freedom of movement" allows citizens of EU member states to live and work in any EU country they please, but it also means once migrants cross over the bloc's external border, they are relatively free to move anywhere within the Eurozone.

"For a lot of people on the right, this is a hugely problematic issue," Springford says.

...Springford says the number of asylum seekers who have arrived over the last several years - between 1.5 and 2 million - should be relatively "easy to absorb" given the European Union population of about 500 million.

"But if we think about it on a political level, it's much more difficult, because a lot of populist politicians have been using the migration issue and using popular frustration about the number of migrants who are coming across, and demanding change, and making it the number-one issue facing society," he says.

..."There's a lot of anti-Donald Trump feeling among the German electorate," Springford tells CBS News. "So it may actually make Germans more steadfast in their determination to keep Europe's borders open and to try and reach a deal on immigration that does not involve just slamming the border shut."