I hadn't paid much attention to Rubio until now, so I figure I'll look into his policy stances using the Google. If you Google a candidate's name, you get a little "On the issues" box that shows you quotes by the candidate on various issues (with links to the articles they're pulled from).
Immigration
Rubio wants to reform immigration by piecemeal legislation, not by one huge bill. He wants to secure our border and get illegal immigration under control, and he wants legal immigration to be based more on merit, less on family.
That all sounds fine to me as long as "secure our border" isn't code for any stupid Trump-like ideas. It doesn't appear to be (he took issue with Trump's statements about immigrants), but it's not exactly clear what it means. I suppose it means increasing funding (i.e., raising taxes) for border control. I'm not sure whether we're currently under-spending or over-spending on border security -- that seems like a complicated question. But in theory, I'm on board with taking cost-effective measures to better prevent illegal immigration while correspondingly increasing legal (and total) immigration. In theory, I also agree with making legal immigration more merit-based, but I'm sure the details are tricky (because family considerations can be important as well).
Bottom line: Google didn't show me any statements by Rubio on this issue that are obviously stupid.
Gun control
Rubio doesn't like gun control. He disagrees with President Obama's executive orders strengthening background checks. I'm not sure of the details of those executive orders and don't really have a position favoring or opposing them, but I find it disappointing that Rubio demagogues the issue by saying that Obama wants to "take away our guns." But, you know, politicians gonna politic.
Bottom line: Whatever.
Gay marriage
Rubio doesn't like gay marriage. That's lame. But at least he doesn't seem particularly rabid about it, and he's not calling for government officials to disobey the Supreme Court or anything; and he supports anti-discrimination laws protecting gays.
Bottom line: He sucks here, but not as much as Cruz et al.
Foreign policy
Rubio doesn't like the Iran deal. He's against ISIS. He likes Israel. He seems a little too interventionist and sanction-happy for my tastes, but foreign policy is hard and I don't have strong opinions about the right course of action in the difficult situations we face.
Bottom line: Meh.
Taxes
He wants to simplify the tax code, like everyone else in the world. He appears to want more tax credits or deductions for having kids ('if corporations get deductions for investing in equipment, why don't families get deductions for investing in children?' - paraphrase). He wants to cut taxes on businesses.
Bottom line: He doesn't seem to have enough of a plan to make it possible to evaluate him on this topic, but what's there (cuts for families and businesses) would seem to reduce revenues, thus increasing the deficit and debt unless there are corresponding reductions in spending (which pretty much never happen).
Health care
He doesn't like Obamacare. Beyond that, the quotes from Google suggest a rather Trumpian plan to make everything fantastic without offering any specifics.
Bottom line: Who knows?
Economy
Supports the TPP. Doesn't think minimum wage hikes are the best way to relieve poverty. Thinks going to college and majoring in philosophy is not always better than going to a trade school.
Bottom line: There's a lot of generic "we need more and better jobs" rhetoric with few specifics, but the few specifics he does offer seem good to me.
Crime
Wants to enforce federal laws against using marijuana. He's concerned about racial profiling and relationships between cops and communities.
Bottom line: Mixed bag, but I think he's dead wrong about the War on Drugs, which I consider to be an extremely important issue.
Environment
He says he's not a climate-change denier, but
who is he kidding? He opposes numerous current and proposed environmental regulations on the grounds that their costs exceed their benefits. I have no idea whether he's right or wrong about that, but he's right to consider both costs and benefits.
Bottom line: Are there any Republicans who depart from the party line on this subject? I don't think so. That's a potential reason not to vote Republican -- though Rubio doesn't seem worse than the others.
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I also skimmed over the stuff on education, national security, entitlements, and energy, but I won't summarize those.
Overall: I'd certainly vote for Rubio over Trump or Cruz. I'd likely vote for Rubio over Hillary. I'd have to give more thought to Rubio versus Bernie. The little I've seen of Rubio in debates and interviews suggests that he's a likable, intelligent, reasonable-minded fellow. On the issues, I agree with him in some areas and disagree in others -- I don't think his nomination would energize me to go to the polls, either to vote for him or to vote against him.