Whatever the case, we the public are definitely as yet in the dark about something. The dots are either really easy or really hard to connect, but fuck if it isn't hard to not start to go down the conspiracy theory rabbit hole. That's a dark place I don't want to visit, but seriously, 0 questions on the matter at hand and a fuckload of questions about "Who is paying you?" followed by the criminal referral you cite. The number of ways to skin this cat are seemingly fewer and fewer. During Watergate it too one reasonable man, John Dean, to flip to get the ball rolling. The GOP closed ranks around Nixon until the tapes came out that confirmed 100% of Dean's testimony. Who's going to be our John Dean, and where are the tapes? None of these people are honorable, and I hope their careers end in shame for them and their families.
When I consider how overt the criminal wrongdoing was in the Watergate breakin, how undeniable the cover-up operation by the administration was--all of it documented by incontrovertible secret tapes--a lot had to "go right" for the House to draw up articles of impeachment. It took over two years from the date of the breakin before Nixon's resignation and it was, by impression, far from inevitable. It makes me wonder if there are stronger headwinds for Mueller's investigation. Supposing that these two episodes in history are analogous, there are probably no audio recordings of Trump et al admitting plainfully their coordination with Russians or illegal profiteering. Then again, Trump strikes me as incomparably more stupid and sloppy than Nixon, and maybe digital bank records and emails are all the "secret tapes" Mueller needs.
"If it's what you say I love it." -Don Jr. in response to an email that was prefaced with, "as part of the Russian government's ONGOING EFFORT TO HELP YOUR FATHER..." And still no questions from the GOP members of the committee. How is an email record that different from tapes? The fact that Jr. didn't say, "If it's what you say, I love it, but wait, why if Russia trying to help my dad? That seems odd." is enough evidence that this wasn't an isolated incident. If that was the first he heard of Russia's effort to elect Trump and he didn't react, then he's literally the stupidest person in public life (since the language was so obviously inserted to use against him if necessary). The other explanation is that it was just routine at that point. Either way the evidence is pretty plain, so maybe even tapes of Trump saying things that even the tin foiliest hatted person in the world couldn't have dreamed up will never be enough....there are probably no audio recordings of Trump et al admitting plainfully their coordination with Russians...
So if GOP heel-dragging is what's gumming up the investigation, what do you see happening if Democrats take over the House in November? (I'm not sure how likely the Senate takeover is. A lot can happen in eleven months but taking the House should be sufficient, no?)
Probably most will refuse. That's when Congress has to sue. This also happened in Watergate. The committee subpoenaed the tapes, and Nixon refused to hand them over (claiming executive privilege). Eventually, the Supreme Court forced the administration to comply. One major difference here is that the Court is occupied by GOP sycophants who have no trouble violating their own stated principles in service of the GOP's agenda. Like with Watergate, getting at the truth will depend entirely on enough Republicans turning on him. If the Grassley/Graham questioning of Fusion GPS is any indication, we have a long way to go. As to your second question, my gut is to not dignify it with an answer. However, it should be pointed out that it is explicitly stated in the Constitution that a member of Congress cannot be arrested when traveling to/from Congress or when in session.