Jeff Sessions is helping Trump with the immigration policy he will present in early September (presumably before the next debate on the 16th).
"Sessions led the fight to stop the immigration expansion effort of 2006 and 2007, before leading the charge to derail the 2013 Gang of Eight bill. Following the 2007 implosion of McCain-Kennedy, the donor class has spent unprecedented sums of money and organizational resources to try to pass legislation that would combine amnesty with a massive increase to record yearly immigration levels. According to a 2013 report from the Sunlight foundation, between 2007 and 2012, lobbying groups spent more than $1.5 billion to pass immigration expansions. The centerpiece of the establishment donor class’s immigration push was the selection of Sen. Marco Rubio (R-FL) as the bill’s chief salesman. In the early days of the Gang of Eight push, when many conservatives were afraid to speak out against Rubio, Sen. Sessions began what started as a lonely one-man fight against the bill– issuing fact-checks on every false statement issued by Rubio’s office. Ultimately, Sen. Sessions succeeded in uniting the conservative movement against the Gang of Eight bill, sending the bill crashing in flames in the House and subsequently stopping Eric Cantor’s plan to pass the same bill in chunks–culminating in the historic loss of the former-House Majority leader at the hands of Congressman Dave Brat (R-VA)."
Donald Trump Consults with Jeff Sessions on Immigration
Breitbart (the website) says if Trump outlines immigration policy specifics along the lines of what Sessions has articulated, polling data suggests that it will not only position Trump to perform well in the Republican primary, but also in the general election.
The story has more details about what Sessions said in his fights against illegal immigration, blue collar workers and the lobbyists but it's all pretty interesting.