How does our government get away with advertising for Obamacare?

I believe this to be a nonpartisan issue.

LINK

Above link says over 600 million of your tax dollars have gone to advertise Obamacare.

How is this legal? By what law is this within the government's ability? Does the Republican leadership in government also have access to tax money to advertise about their concerns about Obamacare?

To drive the point home for my liberal friends....

What if Bush, doing the build up to convince the nation to go to war with Iraq, what if he started advertising the war on national TV? As a liberal, how would you have felt if Kobe Bryant had come on your TV saying he was concerned about the WMDs that Iraq could have? Knowing it was your tax dollars?

My other concern is that this is a small step away from campaigning using tax dollars.

If this has been discussed before, and you have a link, I would read that thread.

If you have other examples of tax money used for advertising partisan issues, I would like to hear it also.