Mitt Romney claims [1] he's more conservative than Donald Trump on immigration. In fact, both support a massive amnesty. Not only that, both make opposing amnesty more difficult by presenting the opposition to it as just something for conservatives.

At a forum in Provo, Utah, Romney took audience questions on index cards. One pointed out that the questioner and their Facebook friends didn't think he was very conservative. Romney said on some issues he's more conservative than Trump:

“For instance, I’m a deficit hawk,” Romney said. “That makes me more conservative than a lot of Republicans and a lot of Democrats. I’m also more of a hawk on immigration than even the president. My view was these DACA kids shouldn’t all be allowed to stay in the country legally.”

...Romney said he is against giving legal residence to those 1.8 million people.

“That was not my posture,” Romney said. “So I was more conservative than others in my party. Now I will accept the president’s view on this, but for me, I draw the line and say, those who’ve come illegally should not be given a special path to citizenship.”

Romney said he believes DACA recipients “need to do more” to justify permanent residency, such as attending community college, getting a degree, serving in the military or serving in needed occupations like teaching.

1. As can be seen at their name links above, both Trump and Romney support amnesty. In the quote above, Romney is supporting amnesty, he just wants to impose conditions on it. Even if amnesty supporters in the GOP and the Democratic Party agreed to Romney's "tough" conditions, they'd start to work to undercut them before the ink was even dry. For instance, "getting a degree" would morph into attending a free class at a local community college. Even if they agreed to a limited amnesty, they'd push to expand it. The amnesties that Trump and Romney want would balloon into something more like what Nancy Pelosi and Charles Schumer want.

2. Those who try to make opposing amnesty and massive/illegal immigration just something for conservatives might as well be working for Nancy Pelosi. Opposing amnesty won't work as just a conservative rallying cry since most Americans aren't conservatives, very few Americans are "Real Conservatives", and many Americans look askance at things conservative. Over the years, opposing amnesty has become a conservative thing, and that's one of the reasons for continuing illegal immigration and the continual pushes for amnesty. If conservatives were any good at opposing amnesty, then there wouldn't be constant pushes for it. To successfully oppose amnesty, the effort has to be "PORS": patriotic, open (as in big tent), rational, and smart. Those leaders who support amnesty have to be marginalized; Romney is marginalizing the opposition to those leaders. If Romney were smart, patriotic, and sincere he'd make arguments that undercut Pelosi etc to their base.

3. Romney is the embodiment of an empty suit. Why he's bothering to run isn't clear: he has enough money and he doesn't really understand policy issues that don't involve business. It can't be out of patriotism; if it were he wouldn't be pushing amnesty or at least he'd be honest about it. He can't be considered a naive dupe for stringpullers since he knows he's trying to deceive. As always, Romney is a mentally and emotionally weak wimp. As before when he's staked out a "tough" stance, expect him to wilt at the pushback (such as the inaccurate "Mitt Romney goes extreme on immigration, attacks DREAMers" [2] from ThinkProgress). In 2012, Romney infamously said illegal aliens should "self-deport". That's a perfectly valid plan called attrition. Because he had pro-amnesty advisors and putatively anti-amnesty advisors that can't defend their ideas, Romney quickly backed off the plan. Romney himself is too intellectually weak to defend what he says and the same is true of his advisors.

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[1] heraldextra · com/news/local/govt-and-politics/elections/at-q-a-in-provo-mitt-romney-says-he-s/article_efee3320-23ac-5435-8c49-ddca54a69fe8.html
[2] thinkprogress · org/mitt-romney-immigration-trump-57a97ec5004d