LONDON — The main route to Europe is experiencing one of its longest lulls since the migration crisis began in 2014.

Just over 4,000 migrants have reached Italy from Libya since mid-July, about a fifth of the number during each of the equivalent periods of 2014, 2015 and 2016, according to the Italian Interior Ministry.

The lull provides rare respite for Italy, where migration — and the center-left government’s response to it — may prove to be a defining factor in a general election in the coming months.

After the European Union reached a deal with Turkey early in 2016 to try to stop migrants reaching the Greek islands in the Mediterranean, Italy once again became the main gateway to Europe — an unwanted title that it has held for most of the 21st century.