Dems introduce legislation that would boost mental health care all the time. You're only looking at the times they do it in response to a shooting. But the thing is, most people don't see "mental health" as part of the "mass shooting" problem, because nobody has ever really connected the two in terms of specific measures. Most people see mental health as a smaller part of health care.
Obamacare increases access to mental health care. Every GOP member voted against it.
The Medicaid expansion would also increase access mental health care access- in fact
Medicaid is the biggest payer of mental health costs in the United States. Not only did the GOP oppose Medicaid expansion at the federal level, but a number of GOP governors turned it down despite the fact that it was basically free for them simply because it was linked to Obama.
A number of them, including Texas, STILL haven't accepted it.
Go to congress.gov and search for mental health bills in the House. You'll find a huge pile of Dem initiatives like
this one that never get off the ground because they can't get any bipartisan support. Go back to the previous Congress, or try the Senate instead of the House?
More of the same.
You wanna pretend that the barriers to improved mental health care are a bipartisan issue, that's your business, but it very clearly is not. If you actually want to see change on this issue I encourage you to vote accordingly.