Remember folks, above all Donald Trump is vindictive. He expects complete subservience and calls it "loyalty", and those who do not meet that standard he either bullies, punishes, or both. Six months into his term and everyone has essentially failed him, and he will fire and replace who he can rid of and terrorize the people he can't. He sees Congress not as a co-equal branch of the government, but as people who work for him that he can't fire (yet.)
But he can punish them for failing him, and he will always start with open threats.
The other part of President Trump's tweet this morning that will get a lot of attention from members of Congress: he hinted he might overturn an Obama-era rule that allows members of Congress and their staffers to get subsidies for their health insurance, which they have to get through an Affordable Care Act health exchange. That's what he meant by "BAILOUTS for Members of Congress."
The back story: The ACA requires members of Congress and their staffs to get health coverage through its exchanges, but it was never clear on whether they should get subsidies to pay for most of their premiums, the way employers pay for most of their workers' health premiums. The Obama administration issued a rule that allowed them to get those subsidies — because if it hadn't, members of Congress worried that talented staffers would leave rather than pay the full cost of the premiums.
But conservative groups have been urging the Trump administration to withdraw the rule, insisting that members of Congress and their staffs shouldn't be shielded from rising ACA premiums. It's now clear that Trump is thinking of taking their advice, although a senior administration source says no final decision has been made.
So for now this is one of Trump's many threats, as that what he feels is "leadership". Whether or not he'll carry through is something else, but this is his M.O. and he'll keep using it as long as it works for him.